Secondary battery charging circuit

ABSTRACT

A secondary battery charging circuit of this invention includes a charging source for supplying a charging current to a secondary battery, a temperature detection unit for generating an output which changes almost linearly with respect to a change in temperature of the secondary battery during a charging operation, a differential unit for obtaining a differential value of an output from the temperature detection unit, a comparator unit for comparing the differential value during the charging operation with a setting value, and for, when the relationship between the two values is reversed, generating an inverted output, a timer circuit unit, started simultaneously with start of the charging operation of the secondary battery, for generating a timer output after an elapse of a predetermined period of time, and a charge control unit for controlling the charging operation of the secondary battery in response to one, generated earlier, of the inverted output from the comparator unit, and the timer output from the timer circuit unit.

This is a division of application Ser. No. 07/775,755, filed on Oct. 15,1991 now U.S. Pat. No. 5,391,974.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a secondary battery charging circuitand, more particularly, to a charging circuit which employs a system forcontrolling a charging operation by detecting the temperature of asecondary battery upon a charging operation.

2. Description of the Related Art

As a system for charging a secondary battery within a short period oftime, it is generally used as following system. When charging iscontrolled at a voltage lowing to ΔV from a peak voltage charged by fastcharging, a secondary battery is charged up to 110% to 120%. On theother hand, when charging is controlled by detecting a batterytemperature using in this invention, a secondary battery is charged upto almost 90% of an electrical capacity of the secondary battery by fastcharging, and thereafter, the remaining capacity of that is charged by aquick or trickle charging operation. The most serious problem in thissystem is determination of a stop timing of fast charging. When the fastcharging operation is unnecessarily continued, the battery temperatureis extremely increased. As a result, the battery is considerably loaded,thus shortening the service life of the battery.

Thus, various charging circuits for detecting a point where thetemperature of a secondary battery is abruptly increased, and stopping afast charging operation have been proposed.

As one of charging circuits utilizing the above-mentioned system, asystem, which utilizes characteristics in that the temperature of asecondary battery is increased in the final period of charging, fordetecting the temperature of a secondary battery by a temperaturesensor, and controlling a charging operation on the basis of thedetection result is known. Examples of this system are as follows.

1) A charging circuit for performing fast charging when the temperatureof a secondary battery is within a predetermined range, and a timedifferential value of temperature is equal to or lower than apredetermined value. In this charging circuit, when the temperature ofthe secondary battery falls within a predetermined range, and the rateof change in temperature is equal to or smaller than a predeterminedvalue, a fast charging current is supplied.

2) A charging circuit for ending charging when the temperature gradientchanges from a negative value or 0 to a positive value. This chargingcircuit has a temperature monitor circuit for monitoring a temperaturerise in accordance with a signal from a temperature sensor incorporatedin a battery, and controlling the charging circuit. When the temperatureof the battery is abnormally increased, the temperature monitor circuitdetects the abnormality of the battery temperature, and controls thecharging circuit, thereby preventing overcharging.

3) A charging circuit for detecting the temperature of a secondarybattery so as to detect a point where the temperature of the secondarybattery is abruptly increased, for comparing the present detectiontemperature and a temperature detected a predetermined period of timebefore, for, when the difference (temperature differential value)reaches a given positive value, determining that fast charging iscompleted. More specifically, an output signal from a temperature sensoris converted into a digital value by an A/D converter to obtaintemperature data, and digital calculations are performed to make theabove-mentioned decision.

However, when a temperature sensor causes an error, or when a connectionerror between the temperature sensor and an electronic circuit occurs,the temperature sensor cannot supply a normal temperature detectionresult to the electronic circuit, and charging end control of thesecondary battery can no longer be performed. As a result, the secondarybattery is overcharged, and its temperature is abnormally increased.Thus, the battery itself or equipment which uses this battery may bedamaged.

In the second example, when a battery such as a nickel-hydrogen batterywhich generates heat from the beginning of charging, and whosetemperature is slightly increased along with charging is to be charged,the temperature gradient turns to a positive value after the battery ischarged only slightly, and the charging operation is ended, resulting ina considerable short charging state. When the fast charging operation ofthe above-mentioned secondary battery is performed when ambienttemperature is high, the battery temperature exceeds a predeterminedvalue before the end of charging, and the charging operation isundesirably ended. As a result, the same state as described above mayoccur.

Furthermore, even when the fast charging operation is started by, e.g.,a switch after the power switch of the charging circuit is turned on,noise components generated by an abrupt change in charging current aremixed in, e.g., a differential circuit, and the same erroneous operationas described above may occur.

Since the conventional charging circuit has only one temperature sensor,when a plurality of batteries connected in series with each other are tobe charged, a change in temperature of one of the batteries is detectedby the temperature sensor to control the charging operation. Therefore,if the batteries include a secondary battery (to be referred to as abattery B hereinafter) having a smaller electrical capacity than that ofa secondary battery (to be referred to as a battery A hereinafter) towhich the temperature sensor is attached, charge control is not startedeven when the temperature of the battery B is increased. Only when thetemperature of the battery A is increased, and the increase intemperature is detected by the temperature monitor circuit, chargecontrol is started. Therefore, the battery B is overcharged. Inparticular, when the difference between the electrical capacities of thebatteries A and B is large, and the batteries A and B are thermallyseparated from each other, the overcharging amount of the battery isincreased. As a result, the battery B causes an abnormal temperaturerise, and may be damaged, or equipment which uses the battery B may bedamaged.

As described above, when the charging circuit has only one temperaturesensor for detecting the temperature of the secondary battery, and whenbatteries connected in series with each other are to be charged, if thebatteries include a secondary battery having a smaller electricalcapacity than that of a secondary battery to which the temperaturesensor is attached, the battery having the smaller electrical capacityis undesirably overcharged.

In the third method, if, for example, an A/D converter included in ameasurement system has a low resolution, a temperature differentialvalue cannot be precisely obtained. More specifically, if the resolutionis low, since a small change in temperature of the secondary batterycannot be detected, a point where the temperature is abruptly increasedin the final period of charging cannot often be detected. As a result,the stop timing of the fast charging operation is delayed, and thebattery is undesirably overloaded. It is preferable to use a 16-bit A/Dconverter. However, a high-resolution A/D converter is expensive, and itis difficult to use such an A/D converter in a charging circuit includedin electronic equipment such as a personal computer, a personalwordprocessor, or the like in view of cost.

As described above, in the conventional charging circuit which measures,as a temperature differential value, a difference between the presentdetection temperature of the secondary battery and a temperaturedetected a predetermined period of time before, and for, when thetemperature differential value reaches a predetermined value, stoppingthe fast charging operation, if the A/D converter or the like in themeasurement system has a low resolution, an abrupt increase intemperature of the secondary battery in the final period of chargingcannot be detected, resulting in overcharging.

References which describe the above-mentioned related arts are asfollows:

1) U.S. Pat. No. 3,852,562 (Published Unexamined Japanese PatentApplication No. 50-44432)

2) U.S. Pat. No. 4,006,397 (Examined Japanese Patent Publication No.56-16631)

3) U.S. Pat. No. 4,045,720

4) U.S. Pat. No. 4,065,712

5) U.S. Pat. No. 4,052,656

6) U.S. Pat. No. 4,670,703

7) U.S. Pat. No. 4,888,544

8) Published Unexamined Japanese Patent Application No. 52-112741

9) Published Unexamined Japanese Patent Application No. 61-161926

10) Published Unexamined Japanese Patent Application No. 61-221538

11) Published Unexamined Japanese Patent Application No. 62-193518

12) Published Unexamined Japanese Patent Application No. 63-76275

13) Published Unexamined Japanese Patent Application No. 1-138931

14) Published Unexamined Japanese Patent Application No. 1-185135

15) Published Unexamined Japanese Patent Application No. 1-186128

16) Published Unexamined Japanese Utility Model Application No. 3-34638

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a secondary batterycharging circuit having high reliability and safety. The presentinvention has the following seven aspects.

(1) Even when a temperature detection system for a secondary batterycannot be normally operated, the secondary battery and equipment can beprevented from being damaged, and even when a secondary battery whichgenerates heat from the beginning of charging, and whose temperature isslightly increased along with charging is to be charged, a propercharging operation can be performed.

(2) A battery can always be charged by a proper amount without causing ashort charging state caused by an erroneous operation due to atemperature rise based on self-heating of a temperature sensorimmediately after the beginning of fast charging, an unstable outputfrom an electronic circuit, or mixing of noise due to an abrupt changein charging current.

(3) A battery can always be charged by a proper amount without causingan erroneous operation due to a temperature rise based on self-heatingof a temperature sensor immediately after the beginning of fastcharging, an unstable output from a differential circuit immediatelyafter power-on, mixing of electrical noise into, e.g., a differentialcircuit during charging, or a change in ambient temperature or aircurrent when a thermal resistance between a temperature sensor andambient temperature is small.

(4) Even when ambient temperature is high, a battery can be charged toalmost 100% of its capacity within a short period of time.

(5) When a charging operation of a plurality of secondary batteriesconnected in series with each other is controlled on the basis of thetemperature of the batteries, an overcharging state can be preventedeven if the secondary batteries have various electrical capacities.

(6) An abrupt increase in temperature of a secondary battery in thefinal period of charging can be reliably detected using an A/D converterhaving a relatively low resolution in a measurement system, and a fastcharging operation can be stopped at a proper timing.

(7) A fast charging mode, a quick charging mode, and a trickle chargingmode are sequentially switched in accordance with a predetermined rateof change in temperature, a predetermined temperature, and apredetermined period of time. Thus, a battery can be charged to almost100% of its capacity within a short period of time. After an elapse ofthe predetermined period of time, the charging method is forciblyswitched, or the charging operation is ended, thus preventingovercharging.

A secondary battery charging circuit according to the first aspect ofthe present invention is characterized by comprising a charging sourcefor supplying a charging current to a secondary battery temperaturedetection unit for generating an output which changes almost linearlywith respect to a change in temperature of the secondary battery duringa charging operation, differential unit for obtaining a differentialvalue of the output from the temperature detection unit, comparator unitfor comparing the differential value during the charging operation and asetting value, and for, when the relationship between the differentialvalue and the setting value is reversed, generating an inverted output,timer circuit unit, started simultaneously with start of the chargingoperation of the secondary battery, for generating a timer output afteran elapse of a predetermined period of time, and charge control unit forcontrolling the charging operation of the secondary battery on the basisof one, generated earlier, of the inverted output from the comparatorunit and the timer output from the timer circuit unit.

In a secondary battery such as a nickel-hydrogen battery, in the initialor middle period of charging, the amount of heat generated inside thebattery is small, and an increase in temperature of the secondarybattery is small. However, in the final period of charging, the amountof heat generated inside the battery is abruptly increased, and asurface temperature is increased until heat generation is balanced withheat radiation. The rate of increase in temperature in the final periodof charging becomes larger as the charging current is larger. However,the rate of increase in temperature is not so influenced by ambienttemperature.

According to the first aspect of the present invention, the chargingcircuit comprises the temperature detection unit whose output almostlinearly changes in accordance with a change in temperature of thesecondary battery, the differential unit for obtaining a differentialvalue of an output from the temperature detection unit, the comparisonunit for comparing the differential value during charging and a settingvalue, and for, when the relationship between the differential value andthe setting value is re versed, generating an inverted output, and thetimer circuit which is started when a charging operation of thesecondary battery is started, and generates a timer output after anelapse of a predetermined period of time. The charging operation of thesecondary battery is controlled on the basis of one, which is outputearlier, of the inverted output from the comparison unit and the timeroutput from the timer circuit. Thus, the charging operation is normallycontrolled by the output from the comparison unit, and even when atemperature detection system including a temperature sensor, thedifferential unit and the comparison unit are defective, or when aconnection error occurs among these units, charge control can beperformed on the basis of a timer output from the timer circuit.

Therefore, an abnormal increase in temperature due to overcharging ofthe secondary battery can be prevented, and hence, the battery andequipment using the battery can be prevented from being damaged, thusimproving reliability and safety.

A secondary battery charging circuit according to the second aspect ofthe present invention is characterized by comprising a charging sourcefor supplying a charging current to a secondary battery, temperaturechange rate detection unit for detecting a rate of change in temperatureof the secondary battery during a charging operation, comparator unitfor comparing an output value from the temperature change rate detectionunit during the charging operation with a setting value, and for, whenthe relationship between the output value and the setting value isreversed, generating an inverted output, charge control unit forstarting the charging operation of the secondary battery in response toa charge start signal, and controlling the charging operation of thesecondary battery on the basis of the inverted output from thecomparator unit, and charge control inhibition unit for inhibitingcharge control by the charge control unit for a predetermined period oftime from the beginning of the charging operation of the secondarybattery.

According to the second aspect of the present invention, the chargingcircuit comprises the temperature change rate detection unit fordetecting a rate of change in temperature of the secondary battery withrespect to time, the comparison unit for comparing the output value fromthe temperature charge rate detection unit during charging and a settingvalue, and for, when the relationship therebetween is reversed,generating an inverted output, and the charge control unit for startinga charging operation of the secondary battery in response to a chargingstart signal, and controlling the charging operation of the secondarybattery in accordance with the inverted output from the comparison unit.In this charging circuit, since the charge control based on the invertedoutput from the comparison unit is inhibited for a predetermined periodof time from the beginning of charging of the secondary battery, anerroneous operation caused by an increase in temperature due toself-heating of a temperature sensor when an arrangement for startingfast charging simultaneously with power-on of the charging circuit isemployed, or caused by an unstable output immediately after power-onwhen an analog differential circuit is used in detection of the rate ofchange in temperature, can be prevented. Furthermore, an erroneousoperation caused by noise generated upon an abrupt change in chargingcurrent at the beginning of charging can also be prevented, and thebattery can always be charged by a proper amount without causing a shortcharging state.

A secondary battery charging circuit according to the third aspect ofthe present invention is characterized by comprising a charging sourcefor supplying a charging current to a secondary battery, temperaturechange rate detection unit for detecting a rate of change in temperatureof the secondary battery during a charging operation, comparator unitfor, when a relationship between an output from the temperature changerate detection unit during the charging operation and a predeterminedsetting value is reversed, generating a comparison output, chargecontrol unit for controlling the charging operation of the secondarybattery in accordance with the comparison output, and signalidentification unit for inhibiting charge control for a predeterminedperiod of time after the comparator unit generates the comparisonoutput.

According to the third aspect of the present invention, the chargingcircuit comprises the temperature change rate detection unit fordetecting a rate of change in temperature of the secondary battery withrespect to time, the comparison unit for comparing the output value fromthe temperature charge rate detection unit during charging and a settingvalue, and for, when the relationship therebetween is reversed,generating a comparison output, and the charge control unit for startinga charging operation of the secondary battery in response to a chargingstart signal, and controlling the charging operation of the secondarybattery in accordance with the comparison output from the comparisonunit. In this charging circuit, since charge control is inhibited by thesignal identification unit for a predetermined period of time after thecomparison unit outputs the comparison output, an erroneous operationcaused by an increase in temperature due to self-heating of atemperature sensor when an arrangement for starting fast chargingsimultaneously with power-on of the charging circuit is employed, anerroneous operation caused by an unstable output immediately afterpower-on of a differential circuit, and an erroneous operation caused bymixing of electrical noise in, e.g., the differential circuit duringcharging or a change in ambient temperature or air current can beprevented, and the battery can always be charged by a proper amount. Asa result, a charging operation can be performed with high reliabilityand safety.

A secondary battery charging circuit according to the fourth aspect ofthe present invention is characterized by comprising a first chargingsource for supplying a charging current to a secondary battery, asecondary charging source for supplying a charging current smaller thanthe charging current supplied from the first charging source to thesecondary battery, switching unit for connecting the first chargingsource to the secondary battery during a first charging period, andconnecting the second charging source to the secondary battery during asecond charging period, first temperature detection unit for detectingthat a temperature of the secondary battery has reached a first settingtemperature, and generating a detection output, second temperaturedetection unit for detecting that a temperature of the secondary batteryhas reached a second setting temperature, and generating a detectionoutput, temperature change rate detection unit for detecting a rate ofchange in temperature of the secondary battery with respect to time,comparator unit for comparing an output value from the temperaturechange rate detection unit during a charging operation to the secondarybattery with a setting value, and for, when the output value reaches thesetting value, generating an inverted output, and control unit forcontrolling a change of charging methods, and stop of the chargingoperation.

The control unit has at least one of units realizing the following threemodes.

(1) When the inverted output from the comparator unit is generatedduring the first charging period, the control unit ends the firstcharging period so as not to substantially start the second chargingperiod, and when the detection output from the first temperaturedetection unit is generated during the first charging period, thecontrol unit starts the second charging period, and ending the secondcharging period in response to one, generated earlier, of the detectionoutput from the second temperature detection unit and the invertedoutput from the comparator unit during the second charging period.

(2) The control unit starts the second charging period in response toone, generated earlier, of the detection output from the firsttemperature detection unit and the inverted output from the comparatorunit during the first charging period, and ends the second chargingperiod in response to one, generated earlier, of the detection outputfrom the second temperature detection unit and the inverted output fromthe comparator unit during the second charging period.

(3) The control unit starts the second charging period in response toone, generated earlier, of the detection output from the firsttemperature detection unit and the inverted output from the comparatorunit during the first charging period, and ends the second chargingperiod in response to the detection output from the second temperaturedetection unit.

A secondary battery, e.g., a nickel-hydrogen battery slightly generatesheat, and its temperature is increased in the initial or middle periodof charging. In the final period of charging, the amount of heatgenerated inside the battery is abruptly increased, and the surfacetemperature is increased until heat generation is balanced with heatradiation. As the charging current is increased, the rate of increase intemperature not only in the final period of charging but also in theinitial or middle period of charging is increased. In particular, whenfast charging is performed when ambient temperature is high, the batterytemperature is abnormally increased.

However, there is a time delay until heat generated inside the batteryreaches the battery surface, and there is also a time delay in responseof a temperature sensor such as a thermistor for detecting the batterytemperature. For this reason, as the charging current becomes larger, alower temperature for stopping fast charging must be set. For thisreason, when ambient temperature is high, a short charging state oftenoccurs.

In the fourth aspect of the present invention, the battery temperatureis detected via the temperature sensor incorporated in or arrangedadjacent to the secondary battery, and in, e.g., the first mode, whenthe rate of increase in temperature of the secondary battery reaches asetting value during a first charging period by a first charging sourceas a fast charging source, the second charging period is set to be zeroor almost zero, thus substantially inhibiting the start of a secondcharging period. When the battery temperature reaches a first settingtemperature during the first charging period, the second charging periodby a second charging source as a quick charging source is started toperform quick charging. Thereafter, when the battery temperature reachesa second setting temperature or when the rate of increase in temperaturereaches the setting value, the second charging period is ended, thusending the quick charging. After the quick charging is ended, forexample, trickle charging is started.

In the second mode, during the first charging period, when the batterytemperature reaches the first setting temperature or when the rate ofincrease in temperature reaches the setting value, the second chargingperiod is started, and during the second charging period, when thebattery temperature reaches the second setting temperature or the rateof increase in temperature reaches the setting value, the secondcharging period is ended.

In the third mode, during the first charging period, when the batterytemperature reaches the first setting temperature or when the rate ofincrease in temperature reaches the setting value, the second chargingperiod is started, and when the battery temperature reaches the secondsetting temperature, the second charging period is ended.

With the above-mentioned charge control, even when the batterytemperature reaches the first setting temperature within a short periodof time like in a case wherein fast charging is performed when ambienttemperature is high, quick charging is performed with a current smallerthan that in the fast charging until the battery temperature reaches thesecond setting temperature higher than the first setting temperature orthe rate of increase in temperature of the battery reaches the settingvalue. Therefore, 100% charging can be performed within a short periodof time. When the rate of increase in temperature reaches the settingvalue in the fast charging, or when the battery temperature reaches thesecond setting temperature in the quick charging, the charging operationis immediately ended. For this reason, overcharging can be prevented,and the secondary battery or equipment using the battery can beprevented from being damaged.

Therefore, even when ambient temperature is high, charging up to almost100% of the capacity can be performed within a short period of time, andan abnormal increase in battery temperature can be prevented, thusprolonging the service life of the battery. Furthermore, the secondarybattery or equipment using the battery can be prevented from beingdamaged, thus improving reliability and safety.

A secondary battery charging circuit according to the fifth aspect ofthe present invention is characterized by comprising a charging sourcefor supplying a charging current to a secondary battery, at least twotemperature sensors for detecting a temperature of the secondarybattery, and generating output signals corresponding to the detectedtemperature, at least two temperature detection unit for respectivelyreceiving the output signals from the at least two temperature sensors,and for, when the detected temperature of the corresponding temperaturesensor reaches a setting value, generating a detection output, andcontrol unit for controlling a charging operation of the secondarybattery in response to a detection output, generated earlier, of thedetection outputs from the at least two temperature detection unit.

According to the fifth aspect of the present invention, since theplurality of temperature sensors are arranged, when a plurality ofsecondary batteries are connected in series with each other, thetemperatures of the batteries can be individually detected. Therefore,since charge control of the secondary batteries is performed in responseto a detection output, generated earliest, of detection outputsgenerated when temperatures detected by the plurality of temperaturesensors reach a setting value, overcharging can be prevented even whenthe plurality of secondary batteries have various electrical capacities.

An output corresponding to one, corresponding to a highest detectiontemperature, of detection outputs which almost linearly change withrespect to changes in detection temperature of the temperature sensorsmay be output, and charge control of the secondary battery may beperformed when the output reaches a setting value. Thus, overchargingcan be similarly prevented.

Furthermore, even when one secondary battery, in particular, a batteryhaving a large electrical capacity, is to be charged, the temperature inthe final period of charging varies depending on the mounting positionof the temperature sensor. In this case, overcharging can be preventedaccording to the present invention.

Therefore, charging can be performed without damaging the secondarybattery or equipment using the battery, thus improving reliability andsafety.

A secondary battery charging circuit according to the sixth aspect ofthe present invention is characterized by comprising a charging sourcefor supplying a charging current to a secondary battery, temperaturedetection unit for detecting a temperature of the secondary battery, andoutputting an electrical signal corresponding to the detectedtemperature, analog-to-digital conversion unit for converting an outputsignal from the temperature detection unit into a digital value, andoutputting the digital value as temperature data, storage unit forsequentially storing a plurality of temperature data at a predeterminedtime interval output from the analog-to-digital conversion unit whileupdating old temperature data, and control unit for, when the number oftemperature data corresponding to differences between one of latesttemperature data and oldest temperature data and the remainingtemperature data of the plurality of temperature data stored in thestorage unit, which differences exceed a predetermined value, reaches apredetermined number, decreasing the charging current from the chargingsource.

According to the sixth aspect of the present invention, since thetemperature of the secondary battery is gradually increased in theinitial period of charging, a difference between latest or oldesttemperature data and other temperature data of a plurality oftemperature data corresponding to battery temperatures stored in astorage unit is small. When the charging operation progresses, andreaches the final period of charging, since the temperature of thesecondary battery is abruptly increased, the difference is abruptlyincreased, and the number of temperature data, in which the differencesexceed a predetermined value, is increased accordingly. Therefore, whenthe number of such temperature data reaches a predetermined value, itcan be reliably determined that the final period of charging has beenreached. At that time, fast charging is stopped, and the chargingcurrent is decreased. As a result, charging up to almost 100% of thecapacity can be performed without causing overcharging.

Furthermore, even when an A/D converter having a relatively lowresolution is used in measurement of temperature data, the end of fastcharging can be reliably determined. Therefore, cost of the chargingcircuit can be reduced.

A secondary battery charging circuit according to the seventh aspect ofthe present invention is characterized by comprising a first chargingsource for supplying a charging current to a secondary battery, a secondcharging source for supplying a charging current smaller than thecharging current from the first charging source to the secondarybattery, a third charging source for supplying a charging currentsmaller than the charging current from the second charging source to thesecondary battery, switching unit for connecting the first chargingsource to the secondary battery during a first charging period,connecting the second charging source to the secondary battery during asecond charging period, and connecting the third charging source to thesecondary battery during a third charging period, first temperaturedetection unit for detecting that a temperature of the secondary batteryhas reached a first setting temperature T₁, and generating a detectionoutput, second temperature detection unit for detecting that thetemperature of the secondary battery has reached a second settingtemperature T₂ higher than the first setting temperature T₁, andgenerating a detection output, third temperature detection unit fordetecting that the temperature of the secondary battery has reached athird setting temperature T₃ higher than the second setting temperatureT₂, and generating a detection output, temperature change rate detectionunit for detecting a rate of change in temperature of the secondarybattery with respect to time, comparator unit for comparing an outputvalue from the temperature change rate detection unit during a chargingoperation to the secondary battery with a setting value, and for, whenthe output value reaches the setting value, generating an invertedoutput, a first timer means started simultaneously with start of thefirst charging period, a second timer mean started simultaneously withstart of the second charging period, a third timer unit startedsimultaneously with start of the third charging period, control unit forstarting the second charging period in response to one, generatedearliest, of the inverted output from the comparator unit, the detectionoutput from the first temperature detection unit, and a timer outputfrom the first timer during the first charging period, starting thethird charging period in response to one, generated earliest, of theinverted output from the comparator unit, the detection output from thesecond temperature detection unit, and a timer output from the secondtimer during the second charging period, and ending the third chargingperiod in response to one, generated earlier, of the detection outputfrom the third temperature detection unit and a timer output from thethird timer during the third charging period, and charge controlinhibition unit for inhibiting charge control upon generation of theinverted output for a predetermined period of time from the beginning ofeach of the first and second charging periods.

After the charging operation is started, a battery test is executed.When no battery abnormality is detected, fast charging is started. Whenan abnormality is detected in the battery, the charging operation isstopped. The abnormality of the battery is detected when a batteryvoltage is abnormally low or high, or when ambient temperature isabnormally low. After the fast charging is started, the fast charging isended when one of the following three conditions is satisfied, andthereafter, quick charging is started.

1) The rate of change in battery temperature exceeds a setting value.

2) The battery temperature exceeds a setting temperature.

3) A setting time of a timer elapses.

After the quick charging is started, the quick charging is ended underthe same conditions as the end conditions of the fast charging, andthereafter, trickle charging is started. In this case, the endconditions of the quick charging may be set independently of those ofthe fast charging.

The trickle charging is ended based on the battery temperature and thesetting time of the timer. The time of the timer may be independentlyset. In this case, the upper limit value of the battery temperature mayuse an upper limit setting value for fast charging and quick charging.For example, the upper limit value of trickle charging may be given by:

    (Temperature Upper Limit Setting Value of Trickle Charging)=2×(Temperature Upper Limit Setting Value of Quick Charging)-(Temperature Upper Limit Setting Value of Fast Charging)

In this manner, a control circuit can be simplified.

According to the seventh aspect of the present invention, the end timingof fast charging and quick charging is determined on the basis of therate of change in temperature and the upper limit value of thetemperature, and the end timing of trickle charging is determined on thebasis of the upper limit value of the temperature. Therefore, sincerespective charging steps can be reliably performed upon detection ofthe temperature and a change in temperature, proper charging can alwaysbe performed. Furthermore, even when an abnormality of a temperaturedetection circuit, a temperature conversion circuit, or the like occurs,since the end timing of each step can be controlled by the timer, safetyand reliability can be guaranteed.

As described above, according to the secondary battery charging circuitsof the first to seventh aspects of the present invention, a secondarybattery can always be charged by a proper amount, and a chargingoperation can be performed with high reliability and safety.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram showing an arrangement of a secondary batterycharging circuit according to the first embodiment of the presentinvention;

FIG. 2 is a circuit diagram showing a detailed arrangement of atemperature conversion circuit unit shown in FIG. 1;

FIG. 3 is a circuit diagram showing a detailed arrangement of adifferential circuit unit shown in FIG. 1;

FIG. 4 is a circuit diagram showing a modification of the temperatureconversion circuit unit shown in FIG. 2;

FIGS. 5A to 5C are graphs showing charging characteristics forexplaining an operation of the circuit shown in FIG. 1;

FIG. 6 is a block diagram showing an arrangement of a secondary batterycharging circuit according to the second embodiment of the presentinvention;

FIGS. 7A and 7B are graphs showing charging characteristics forexplaining an operation of the circuit shown in FIG. 6;

FIG. 8 is a circuit diagram of principal part in the first modificationof the second embodiment;

FIG. 9 is a circuit diagram of principal part in the second modificationof the second embodiment;

FIG. 10 is a circuit diagram of principal part in the third modificationof the second embodiment;

FIG. 11 is a block diagram showing an arrangement of a secondary batterycharging circuit according to the third embodiment of the presentinvention;

FIG. 12 is a circuit diagram showing a detailed arrangement of a controlcircuit unit shown in FIG. 11;

FIG. 13A is a graph showing charging characteristics of a differentialoutput;

FIG. 13B is a graph showing charging characteristics of a comparisonoutput;

FIG. 13C is a graph showing charging characteristics of a first timeroutput;

FIG. 13D is a graph showing charging characteristics of a NOR gateoutput;

FIG. 14 is a block diagram showing another detailed arrangement of asignal identification circuit unit;

FIG. 15 is a block diagram showing an arrangement of a secondary batterycharging circuit according to the fourth embodiment of the presentinvention;

FIG. 16 is a circuit diagram showing a detailed arrangement of a signalidentification circuit unit shown in FIG. 15;

FIGS. 17A to 17C are waveform charts for explaining operations at lowtemperature and at normal temperature in the fourth embodiment;

FIGS. 18A to 18C are waveform charts for explaining operations at hightemperature in the fourth embodiment;

FIG. 19 is a circuit diagram showing a modification of a control circuitunit in the fourth embodiment of the present invention;

FIG. 20 is a circuit diagram showing a secondary battery chargingcircuit according to the fifth embodiment of the present invention;

FIGS. 21A to 21F are graphs showing charging characteristics forexplaining an operation of the circuit shown in FIG. 20;

FIG. 22 is a circuit diagram showing a secondary battery chargingcircuit according to a modification of the fifth embodiment of thepresent invention;

FIG. 23 is a circuit diagram showing a detailed arrangement of a signalprocessing circuit unit shown in FIG. 22;

FIGS. 24A to 24E are graphs showing charging characteristics forexplaining an operation of the circuit shown in FIG. 22;

FIG. 25 is a circuit diagram showing an arrangement of a secondarybattery charging circuit according to the sixth embodiment of thepresent invention;

FIG. 26 shows in detail a map of a memory shown in FIG. 25;

FIG. 27 is a graph for explaining the operation of the sixth embodiment;

FIG. 28 is a block diagram showing an arrangement of a secondary batterycharging circuit according to the seventh embodiment of the presentinvention; and

FIG. 29 is a chart showing an operation of the circuit shown in FIG. 28.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an arrangement of a secondary batterycharging circuit according to the first embodiment of the presentinvention.

In FIG. 1, the secondary battery charging circuit of this embodimentcomprises a battery charging source 200, a charge control circuit unit300, a temperature detection unit 100 including a temperature sensor 110and a temperature conversion circuit unit 120, a differential circuitunit 400, a voltage comparator unit 500, and a timer circuit unit 600.The temperature detection unit 100 and the differential circuit unit 400constitute a temperature change rate detection unit 450.

The battery charging source 200 is connected to a secondary battery 10(to be referred to as a battery hereinafter), e.g., a nickel-hydrogenbattery. As the battery charging source 200, a power supply forobtaining a DC current by rectifying an output from an AC power supply,or another battery having a relatively large capacity is used.

The temperature sensor 110 (arranged in or adjacent to the battery 10)detects the temperature of the battery 10.

The temperature conversion circuit unit 120 converts an output from thetemperature sensor 110 into a voltage output value V_(t) which changesalmost linearly, i.e., almost proportional to a change in temperature.

FIG. 2 shows the circuit arrangement of the temperature conversioncircuit unit 120. In FIG. 2, a thermistor Th is used as the temperaturesensor 110. The thermistor Th has two input terminals. One inputterminal a is applied with a reference voltage V_(ref). The other inputterminal b is grounded through a resistor R, and is connected to anoutput terminal c. The resistance of the thermistor Th is nonlinearlydecreased as the temperature increases. However, when the resistance ofthe resistor R is appropriately selected in correspondence with thecharacteristics of the thermistor Th, a voltage output V_(t) almostproportional to the detection temperature of the thermistor Th can beobtained from the output terminal c.

The output from the temperature detection unit 100 is input to thedifferential circuit unit 400, and is differentiated by the differentialcircuit unit 400.

FIG. 3 shows the circuit arrangement of the differential circuit unit400. The differential circuit unit 400 comprises an operationalamplifier 410 whose inverting input terminal receives a referencevoltage (a ground potential in this embodiment), a series circuit of acapacitor C₁ and a resistor R₂ connected between the operationalamplifier and an input terminal a, and a parallel circuit of a capacitorC₂ and a resistor R₃ connected between the inverting input terminal andthe output terminal of the operational amplifier 410. The outputterminal of the operational amplifier 410 serves as an output terminal bof the differential circuit unit 400. In the differential circuit unit400, respective constants are selected, so that the rate of change intemperature (in particular, the rate of increase in temperature) of thebattery 10 can be detected. As has been described above with referenceto FIG. 2, the resistance of the thermistor Th is nonlinearly decreasedas the temperature increases. However, the output voltage V_(t) from thetemperature detection unit 100 changes almost inversely proportional tothe temperature. When the output value V_(t) from the temperaturedetection unit 100 is differentiated by the differential circuit unit400, a differential output Vo is given by:

    V.sub.o =-C.sub.1 ·R.sub.3 dVt/dt

when the temperature increases, Vo also has a positive value. Theresistor R₂ and the capacitor C₂ are used for stably operating thedifferential circuit unit 400.

The thermistor Th constituting the temperature detection unit 100 andthe resistor R in the temperature conversion circuit unit 120 shown inFIG. 2 may be connected by replacing the positions of the thermistor Thand the resistor R in the temperature conversion circuit unit 120, sothat a voltage almost inversely proportional to a battery temperaturedetected by the thermistor Th is generated, as shown in FIG. 4. In thecircuit shown in FIG. 4, the voltage comparator unit 500 may compare anoutput V_(t) ' from the differential circuit unit 400 with a settingvalue V_(k), and may output an inverted output when V_(t) '<V_(k) isestablished.

The output from the differential circuit unit 400 is input to one inputterminal of the voltage comparator unit 500 having two input terminals.The other input terminal of the voltage comparator unit 500 receives thesetting value V_(k). When a differential value as the output from thedifferential circuit unit 400 exceeds the setting value V_(k), thevoltage comparator unit 500 generates an inverted output indicating thatthe rate of increase in temperature of the battery 10 has reached a rateof increase in temperature corresponding to the setting value V_(k).

The timer circuit unit 600 is started simultaneously with the start ofcharging, and generates a timer output after an elapse of apredetermined period of time (timer time). The output terminal of thetimer circuit unit 600 is connected to a control terminal of the chargecontrol circuit unit 300 together with the output terminal of thevoltage comparator unit 500.

The charge control circuit unit 300 comprises, e.g., a switching circuitor a parallel circuit of a switching circuit and a resistor. In a normalcharging state, the switching circuit is set in an ON state. Theswitching circuit is set in an OFF state, i.e., a charge control statewhen a predetermined signal is supplied to the control terminal. In thecharge control state, control for completely stopping the chargingoperation of the battery 10 or decreasing the charging current isperformed.

The operation of the charging circuit shown in FIG. 1 will be describedbelow with reference to the charging characteristic graphs shown inFIGS. 5A to 5C.

FIG. 5A shows changes in terminal voltage (battery voltage) V_(B) andtemperature (battery temperature) TB over time after charging isstarted, FIG. 5B shows a change in output V_(t) from the temperatureconversion circuit unit 120 over time after charging is started, andFIG. 5C shows a change in output (differential value) V_(t) ' from thedifferential circuit unit 400 over time after charging is started.

when a charging operation is started, the battery charging source 200begins to supply a charging current to the battery 10 via the chargecontrol circuit unit 300. When the current is supplied to the battery10, the battery voltage V_(B) is increased accordingly. The batterytemperature T_(B) is almost constant or linearly increased by a smallamount.

As the charging operation progresses and reaches the final period ofcharging, the temperature of the battery 10 begins to abruptly increase.The temperature of the battery 10 is converted into an electrical signalby the temperature sensor 110, and the electrical signal is convertedinto a voltage output V_(t) drawn by real line almost proportional tothe temperature by the temperature conversion circuit unit 120 shown inFIG. 2. The temperature conversion circuit 120 shown in FIG. 4 convertsa temperature to a voltage output V_(t) ' drawn by dot line. The outputV_(t) from the temperature conversion circuit unit 120 is input to thedifferential circuit unit 400, and a voltage differential valuecorresponding to a rate of increase in temperature of the battery 10with respect to time is output as an output V_(t) ' from thedifferential circuit unit 400. The output V_(t) ' from the differentialcircuit unit 400 is a zero or small positive voltage in the initial ormiddle period of charging, and is abruptly increased in the final periodof charging.

By using the temperature conversion circuit unit 120 shown in FIG. 4,the temperature conversion circuit unit 120 output V_(t) ' indicated bydot line, and the voltage comparator unit 500 compares the output V_(t)' from the differential circuit unit 400 with the setting value V_(k),and generates an inverted output when V_(t) '>V_(k) is established. Byusing the temperature conversion circuit unit 120 shown in FIG. 2, thevoltage comparator unit 500 compares the output V_(t) ' from thedifferential circuit unit 400 with the setting value V_(k), andgenerates an inverted output when V_(t) '<V_(k) is established. Theinverted output is input to the charge control circuit unit 300, therebysetting the charge control circuit unit 300 in the charge control state.When the charge control circuit unit 300 is set in the charge controlstate, since the switching circuit is set in an OFF state, control forstopping the charging operation, or control for decreasing the chargingcurrent upon insertion of a resistor in a charging path is executed bythe charge control circuit unit 300.

A normal charging operation is performed, as described above.

If an abnormality occurs in the temperature sensor 110, the temperatureconversion circuit unit 120, the differential circuit unit 400, thevoltage comparator unit 500, and the like, or if a connection erroramong these units occurs, and the rate of increase in temperature of thebattery 10 reaches a value for causing the output V_(t) ' from thedifferential circuit unit 400 to reach the setting value V_(k), theinverted output from the voltage comparator unit 500 cannot be normallysupplied to the charge control circuit unit 300. In this case, the timercircuit unit 600 outputs a timer output after an elapse of thepredetermined period of time, and the timer output is input to thecharge control circuit unit 300. In response to the timer output, thecharge control circuit unit 300 is set in the charge control state, thusperforming control for stopping the charging operation or control fordecreasing the charging current, as described above.

Since the timer circuit unit 600 is arranged in this manner, even if anabnormality occurs in a circuit, e.g., the temperature sensor 110, thetemperature conversion circuit unit 120, the differential circuit unit400, the voltage comparator unit 500, and the like, or if a connectionerror occurs among these units, the charge control circuit unit 300 canbe set in the charge control state in response to the timer output fromthe timer circuit unit 600. Therefore, according to the first aspect ofthe present invention, the temperature of the battery 10 can beprevented from being abnormally increased due to overcharging.

FIG. 6 is a block diagram showing an arrangement of a charging circuitaccording to the second embodiment of the present invention.

In this embodiment, a difference from the first embodiment is that aninitial setting circuit unit 700 and a flip-flop circuit unit 310 arearranged. The same reference numerals as in the first embodiment denotethe same units in the second embodiment, and a detailed descriptionthereof will be omitted (the same applies to the following third toseventh embodiments). In the second to seventh embodiments, the timercircuit unit 600 is omitted. However, the timer circuit unit 600 can beemployed to improve safety like in the first embodiment.

The temperature of a battery 10 is detected by a temperature change ratedetection unit 450, and is subjected to predetermined processing. Thedetected temperature is then output to a voltage comparator unit 500.Thereafter, predetermined processing is performed in the voltagecomparator unit 500 in the same manner as in the first embodiment.

The output from the voltage comparator unit 500 is input to the firstinput terminal of a NOR gate 720 of the initial setting circuit unit 700via a terminal a. The initial setting circuit unit 700 is constitutedby, e.g., the NOR gate 720 and a delay timer circuit unit 710. The delaytimer circuit unit 710 is started in response to a start pulse (chargingstart signal) input via a terminal b, and the output terminal of thedelay timer circuit unit 710 is connected to the second input terminalof the NOR gate 720. An output terminal c of the NOR gate 720corresponding to the output terminal of the initial setting circuit unit700 is connected to a reset input terminal R of the flip-flop circuitunit 310, and a set input terminal of the flip-flop circuit unit 310receives the start pulse. An output terminal Q of the flip-flop circuitunit 310 is connected to a control terminal of a charge control circuitunit 300.

The operation of the charging circuit shown in FIG. 6 will be describedbelow with reference to the charging characteristic graphs shown inFIGS. 7A and 7B.

FIG. 7A shows a change in differential output Vo from a differentialcircuit unit 400 over time after charging is started, and FIG. 7B showsa change in output from the delay timer circuit unit 710 over time aftercharging is started. Changes in terminal voltage V_(B) and temperatureT_(B) of the battery 10 over time after charging is started are as shownin FIG. 5A.

When a start pulse generated in response to a power-on or switch-onoperation of the charging circuit is applied to the set input terminal Sof the flip-flop circuit unit 310, the output terminal Q of theflip-flop circuit unit 310 goes to high level, and the charge controlcircuit unit 300 is set in a fast charging state. When the fast chargingstate is set, a large current is supplied from a battery charging source200 to the battery 10, thus starting fast charging.

The start pulse is also supplied to the terminal b of the initialsetting circuit unit 700 to start the delay timer circuit unit 710. Theoutput from the delay timer circuit unit 710 goes to high level for onlya predetermined period of time t a after the unit 710 is started, andthen goes to low level after an elapse of the predetermined period oftime. The output is output to the second input terminal of the NOR gate720.

The output Vo from the differential circuit unit 400 often exceeds thesetting value V_(k) due to self-heating of the temperature sensor 110 oran abrupt change in charging current of the capacitor in thedifferential circuit unit 400 in the initial period of charging, i.e.,during a period between start time t=0 until time t_(b), as shown inFIG. 7A. In a case shown in FIG. 7A, the voltage comparator unit 500generates an inverted output during period between t=0 until time t_(b).

When the timer time t a of the delay timer circuit unit 710 is set tosatisfy t_(a) >t_(b), as shown in FIG. 7B, the second input terminal ofthe NOR gate 720 is kept at high level during the timer time t_(a). Forthis reason, even when the voltage comparator unit 500 outputs alow-level inverted output during a period between t=0 and time t_(b),and the inverted output is applied to the first input terminal of theNOR gate 720, the output from the NOR gate 720 is kept at low level.Therefore, the output terminal Q of the flip-flop circuit unit 310 iskept at high level, and the charge control circuit unit 300 can maintainthe fast charging state.

when the charging operation progresses and reaches the final period ofcharging after time t=t_(a), the temperature T_(B) of the battery 10begins to immediately increase, and the output Vo from the temperaturechange rate detection unit 450 corresponding to the rate of change ofthe temperature rise is increased, as shown in FIG. 7A. When the outputVo from the differential circuit unit 400 exceeds the setting valueV_(k) when t=t_(c), the voltage comparator unit 500 generates alow-level inverted output. At this time, the timer time t_(a) hasalready elapsed in the delay timer circuit unit 710, and the output fromthe unit 710 is set at low level. Thus, both the input terminals of theNOR gate 720 go to low level, and the output from the NOR gate 720 goesto high level. Therefore, when the reset terminal R of the flip-flopcircuit unit 310 goes to high level, the output terminal Q of theflip-flop circuit unit 310 goes to low level, as a result, the chargecontrol circuit unit 300 is set in the charge control state.

Modifications of the initial setting circuit unit 700 will be describedhereinafter with reference to FIGS. 8 to 10.

FIG. 8 shows the first modification of the initial setting circuit unit700.

The initial setting circuit unit 700 of the first modification includesthe flip-flop circuit unit 310 shown in FIG. 6. The flip-flop circuitunit 310 comprises NOR gates 311A and 311B, and a NOT gate 312. The setinput terminal S is connected to one input terminal of the NOR gate311A, and the reset input terminal R is connected to one input terminalof the NOR gate 311B. The other input terminal of the NOR gate 311A isconnected to the output terminal of the NOR gate 311B, and the otherinput terminal of the NOR gate 311B is connected to the output terminalof the NOR gate 311A. The output terminal of the NOR gate 311A isconnected to the input terminal of the NOT gate 312, and the outputterminal of the NOT gate 312 serves as the output terminal c of theinitial setting circuit unit 700. The set input terminal S of theflip-flop circuit unit 310 is connected to the output terminal of thedelay timer circuit unit 710, and the delay timer circuit unit 710 andthe flip-flop circuit unit 310 constitute the initial setting circuitunit 700.

According to the arrangement shown in FIG. 8, when both the set andreset input terminals S and R of the flip-flop circuit unit 310simultaneously go to high level, the status of the set input terminal Sis preferentially used, and the output terminal Q goes to high level.When a start pulse is input to the input terminal b of the initialsetting circuit unit 700, the delay timer circuit unit 710 is started,and the output terminal of the delay timer circuit unit 710 is kept athigh level for a predetermined period of time t_(a). This high-leveloutput is input to the set input terminal S of the flip-flop circuitunit 310. Thus, the output terminal Q of the flip-flop circuit unit 310goes to high level, and the charge control circuit unit 300 is set inthe fast charging state.

Assume that the output Vo from the differential circuit unit 400 exceedsthe setting value V_(k) due to self-heating of the temperature sensor110 or an abrupt change in charging current of the capacitor in thedifferential circuit unit 400 before time t_(a) from the beginning ofcharging, and the voltage comparator unit 500 generates a high-levelinverted output (in this case, the input terminals of the voltagecomparator unit 500 are assumed to be connected to sides opposite tothose shown in FIG. 6, i.e., the non-inverting input terminal isconnected to the output terminal of the differential circuit unit 400,and the inverting input terminal is applied with the setting valueV_(k)). Thus, even when one input terminal of the NOR gate 311B goes tohigh level, since the output terminal of the delay timer circuit unit710 is at high level, the output terminal Q of the flip-flop circuitunit 310 is kept at high level, and the charge control circuit unit 300maintains the fast charging state.

FIG. 9 shows the second modification of the initial setting circuit unit700.

The initial setting circuit unit 700 shown in FIG. 9 comprises the delaytimer circuit unit 710, and two switch elements 711A and 711B. Theswitch elements 711A and 711B are respectively connected in parallelwith the resistors R₂ and R₃ of the differential circuit unit 400. Theswitch elements 711A and 711B can comprise, e.g., semiconductor switchessuch as bipolar transistors, field effect transistors, and the like, ormechanical switches such as lead switches. When the delay timer circuitunit 710 is started in response to a start pulse generated at thebeginning of charging, the switch elements 711A and 711B are set in anON state. When the switch elements 711A and 711B are set in an ON state,the resistors R₂ and R₃ constituting a time constant element togetherwith the capacitors C₁ and C₂ in the differential circuit unit 400 areshort-circuited, thereby setting a small time constant. In this manner,after the charging circuit is powered, the output from the operationalamplifier 410 in the differential circuit unit 400 (i.e., the outputfrom the differential circuit unit 400) can be immediately stabilized.Thus, even when the output value V_(t) from the temperature conversioncircuit unit 120 is changed due to self-heating of the temperaturesensor 110, the output from the operational amplifier 410 is almostzero, and no inverted output is generated.

FIG. 10 shows the third modification of the initial setting circuit unit700.

The initial setting circuit unit 700 shown in FIG. 10 comprises thedelay timer circuit unit 710 and a switch element 711. The switchelement 711 is connected between a node between the capacitor C₁ and theresistor R₂, and the non-inverting input terminal of the operationalamplifier 410 of the differential circuit unit 400, and is set in an ONstate for only a predetermined period of time t a at the beginning ofcharging in accordance with the output from the delay timer circuit unit710. In FIG. 10, since one terminal of the capacitor C₁ on the side ofthe resistor R₂ is grounded through the switch element 711 at thebeginning of charging, a small time constant is set like in the circuitshown in FIG. 9, and the same effect as in the circuit shown in FIG. 9can be obtained.

FIG. 11 shows a secondary battery charging circuit according to thethird embodiment of the present invention.

A difference between this embodiment and the first embodiment is that asecond timer circuit unit 715, a signal identification circuit unit 800,and a flip-flop circuit unit 310 are arranged between a voltagecomparator unit 500 and a charge control circuit unit 300.

In FIG. 11, a battery temperature is detected, and the detection outputsubjected to predetermined processing in a temperature change ratedetection unit 450 is compared with a predetermined voltage, therebyoutputting an inverted output from the voltage comparator unit 500 likein the first embodiment.

The output from the voltage comparator unit 500 is connected to thesignal identification circuit unit 800. FIG. 12 shows a circuitarrangement of the signal identification circuit unit 800. In FIG. 12,the output from the voltage comparator unit 500 is connected to theinput terminal of the signal identification circuit unit 800. The inputterminal of the signal identification circuit unit 800 is connected tothe first input terminal of a NOR gate 810, and is also input to a firsttimer circuit unit 820 via a time constant circuit constituted by aresistor R₆ and a capacitor C₃. The second input terminal of the NORgate 810 is connected to the output terminal of the first timer circuitunit 820. The output terminal of the NOR gate 810 is connected to anintegration circuit constituted by a resistor R7 and a capacitor C4, andthe output from the integration circuit is connected to a first resetterminal R1 of the flip-flop circuit unit 310 via the output terminal ofthe signal identification circuit unit 800. The integration circuitconstituted by the resistor R7 and the capacitor C4 is used forabsorbing a hazard component generated due to a shift between timings ofsignals applied to the two input terminals of the NOR gate 810.

The flip-flop circuit unit 310 has three input terminals, i.e., a setterminal S and reset terminals R1 and R2, and one output terminal Q, andis constituted by a NOR gate 311A having two input terminals, a NOR gate311B having three input terminals, and a NOT gate 312. In the flip-flopcircuit unit 310 of this embodiment, the number of input terminals ofthe NOR gate 311B of the flip-flop circuit unit 310 shown in FIG. 8 isincreased to three, and the operation is the same as that of theflip-flop circuit unit 310 shown in FIG. 8.

The reset terminal R2 of the flip-flop circuit unit 310 is connected tothe output terminal of the second timer circuit unit 715 which isstarted in response to a start pulse. The start pulse is also applied tothe set input terminal S of the flip-flop circuit unit 310. The secondtimer circuit unit 715 outputs a timer output for forcibly executingcharge control when control by the temperature change rate detectionunit 450, the voltage comparator unit 500, and the signal identificationcircuit unit 800 cannot be normally operated. The output terminal Q ofthe flip-flop circuit unit 310 is connected to a control terminal of thecharge control circuit unit 300.

The charge control circuit unit 300 is set in a fast charging state whenthe output terminal Q of the flip-flop circuit unit 310 is at highlevel, and is set in a charge control state when the terminal Q is atlow level. In the charge control state, the charge control circuit unit300 completely stops charging of a battery 10 or decreases the chargingcurrent.

The operation of the charging circuit shown in FIG. 11 will be describedbelow with reference to charging characteristic graphs shown in FIGS.13A to 13D.

Changes in terminal voltage V_(B) and temperature T_(B) of the battery10 over time after charging is started are as shown in FIG. 5A.

In FIG. 11, when a start pulse generated in response to a power-on orswitch-on operation of the charging circuit is applied to the setterminal S of the flip-flop circuit unit 310, the output terminal Q ofthe flip-flop circuit unit 310 goes to high level, and the chargecontrol circuit unit 300 is set in a fast charging state. In this case,a battery charging source 200 supplies a large current to the battery10, thus starting fast charging.

An output Vo from a differential circuit unit 400 may often exceed thesetting value V_(k) due to self-heating of a temperature sensor 110,charging of a capacitor in the differential circuit unit, an abruptchange in charging current, or the like in the initial period ofcharging, i.e., in a period between start time t=0 and time t_(a), asindicated by a solid curve in FIG. 13A, and the voltage comparator unit500 may generate a comparison output. During charging, an output fromthe temperature sensor 110 may often be changed due to electrical noise,a small thermal resistance between the temperature sensor 110 and thebattery 10, or a change in ambient temperature or air current, and apeak A may appear in a differential output, as shown in FIG. 13A. Inthis case, a comparison output may be generated during a period betweent_(b) and t_(c), as shown in FIG. 13B. However, as shown in FIG. 13C,the output from the first timer circuit unit 820 goes to high levelduring t_(a) after the comparison output is generated, and if t_(b)<t_(a) and t_(c) <t_(a) are satisfied, the output from the NOR gate 810is kept at low level. Thus, the charge control circuit unit 300maintains a fast charging state.

When the charging operation progresses and reaches the final period ofcharging, and when the battery temperature is abruptly increase, asshown in FIG. 5A, a differential output is also increased, as shown inFIG. 13A. When the differential output exceeds a setting value V_(k) attime t=t_(d) upon an increase in differential output, the comparisonoutput is generated, and the output from the first timer circuit unit820 goes to high level during a period between t=t_(d) and t_(a). Afteran elapse of the timer time of the first timer circuit unit 820, whent>t_(d) +t_(a) is satisfied, both the signals input to the two inputterminals of the NOR gate 810 go to low level. Thus, the output from theNOR gate 810 goes to high level, and the output Q from the flip-flopcircuit unit 310 goes to low level. As a result, the charge controlcircuit unit is set in the charge control state.

The second timer circuit unit 715 is started simultaneously with thebeginning of fast charging. If a temperature change rate detectioncircuit, or the like cannot be normally operated, and if the resetterminal R1 of the flip-flop circuit unit 310 does not go to high levelafter time t=t_(d) +t_(a), and fast charging continues, the resetterminal R2 of the flip-flop circuit unit 310 goes to high level inresponse to the timer output from the second timer circuit unit 715.Thus, the output Q from the flip-flop circuit unit 310 goes to lowlevel, and the charge control circuit unit 300 is set in the chargecontrol state. As a result, the battery can be prevented from beingconsiderably overcharged.

FIG. 14 shows a modification of the signal identification circuit unit800. The input terminal c of the signal identification circuit unit 800is connected to the input terminal of a NOT gate 830, and is alsoconnected to the first timer circuit unit 820 via a time constantcircuit constituted by the resistor R₆ and the capacitor C₃. The outputterminal of the NOT gate 830 is connected to an output terminal e of thesignal identification circuit unit 800, and the output terminal of thefirst timer circuit unit 820 is connected to an output terminal f of thesignal identification circuit unit 800.

In the flip-flop circuit unit 310 of this modification, the flip-flopcircuit unit 310 shown in FIG. 8 is modified to have two set inputterminals and two reset input terminals. That is, the flip-flop circuitunit 310 has two set terminals S1 and S2, two reset terminals R1 and R2,and an output terminal Q, and is constituted by NOR gates 311A and 311B,and a NOT gate 312. A reset signal R1 is connected to the first inputterminal of the NOR gate 311B, and a reset signal R2 is connected to thesecond input terminal of the NOR gate 311B. The third input terminal ofthe NOR gate 311B is connected to the output terminal of the NOR gate311A and the input terminal of the NOT gate 312. The first inputterminal of the NOR gate 311A is connected to the input terminal of theNOR gate 311B, the second input terminal thereof is connected to the setterminal S1 of the flip-flop circuit unit 310, and the third inputterminal thereof is connected to the set terminal S2 of the flip-flopcircuit unit 310. The output terminal of the NOT gate 312 is connectedto the output terminal Q of the flip-flop circuit unit 310. When the setterminal S1 or S2 and the reset terminal R1 or R2 of the flip-flopcircuit unit 310 simultaneously go to high level, the set signal ispreferentially received, and the output terminal Q goes to high level.

The set terminal S1 of the flip-flop circuit unit 310 is connected tothe output terminal f of the signal identification circuit unit 800, andthe reset terminal R1 thereof is connected to the output terminal e ofthe signal identification circuit unit 800. The reset terminal R2 isconnected to the output terminal of the second timer circuit unit 715which is started in response to a start pulse. The start pulse is alsoapplied to the set terminal S2 of the flip-flop circuit unit 310. Thesecond timer circuit unit 715 is used for forcibly executing chargecontrol in response to its timer output when control by the temperaturechange rate detection unit, the comparator unit, and the signalidentification circuit unit cannot be normally operated. The outputterminal Q of the flip-flop circuit unit 310 is connected to the chargecontrol circuit unit 300.

In FIG. 14, when a comparison output is generated from the voltagecomparator unit 500, and is applied to the input terminal c of thesignal identification circuit unit 800, a high-level signal from the NOTgate 830 is applied to the reset terminal R1 of the flip-flop circuitunit 310 via the output terminal e of the signal identification circuitunit 800. However, the first timer circuit unit 820 is started via thetime constant circuit constituted by the resistor R₆ and the capacitorC₃ simultaneously with generation of the comparison output, and itsoutput is set at high level for only a time t_(a). Therefore, when thecomparison output disappears before an elapse of the time t_(a) fromgeneration of the comparison output from the voltage comparator unit500, since a high-level signal is applied to the set terminal S1 of theflip-flop circuit unit 310 via the output terminal f of the signalidentification circuit unit 800, the output terminal Q of the flip-flop310 is kept at high level, and the charge control circuit unit maintainsthe fast charging state. If the comparison output is kept generatedafter an elapse of the time t_(a) from generation of the comparisonoutput from the voltage comparator unit 500, both the set terminals S1and S2 of the flip-flop circuit unit 310 go to low level, and the resetterminal R1 goes to high level. Therefore, the output terminal Q of theflip-flop circuit unit 310 goes to low level, and the charge controlcircuit unit 300 is set in the charge control state.

In FIG. 11, the temperature change rate detection unit comprises theanalog differential circuit including the resistor, the capacitor, andthe operational amplifier. However, the output from the temperaturedetection unit may be measured at every predetermined time t_(c), adifference A of a measurement value from a previous measurement value iscalculated, and when the difference A exceeds a setting value, chargingmay be controlled.

FIG. 15 is a block diagram of a charging circuit according to the fourthembodiment of the present invention.

Differences between this embodiment and the first embodiment are thattwo battery charging sources are arranged, voltage comparator units 510and 520, and a control circuit unit 850 are arranged between a voltagecomparator unit 500 and a charge control circuit unit 300, and aswitching circuit 320 is arranged in place of the charge controlcircuit.

First and second charging sources 200A and 200B are selectivelyconnected via the switching circuit 320 consisting of two switches SW1and SW2. The switches SW1 and SW2 can comprise, e.g., transistors,thyristors, relays, or the like. The first charging source 200A is usedfor fast charging, and the second charging source 200B is used for quickcharging. Each of these charging sources obtains a DC output byrectifying an output from an AC power supply, or comprises anotherbattery having a relatively large capacity. Note that the output currentof the second charging source 200B is lower than that of the firstcharging source 200A.

An output terminal c of a temperature detection unit 100 is connected toan input terminal d of a temperature change rate detection unit 450. Anoutput terminal e of the temperature change rate detection unit 450 isconnected to the non-inverting input terminal of the voltage comparatorunit 500.

The output terminal c of the temperature detection unit 100 is alsoconnected to the inverting input terminal of the voltage comparator unit510. The non-inverting input terminal of the voltage comparator unit 510is applied with a reference voltage V_(k3), and the voltage comparatorunit 510, a generator (not shown) for generating the reference voltageV_(k3), and the temperature detection unit 100 constitute a firsttemperature detection unit. In the first temperature detection unit,when a temperature detected by a thermistor Th is increased, and anoutput V_(t) from a temperature conversion circuit unit 120 is decreasedand reaches V_(k3), the output from the voltage comparator unit 510 isinverted from low level to high level, thereby generating a detectionoutput indicating that the temperature of a battery 10 has reached afirst setting temperature corresponding to the setting value V_(k3).

The output terminal c of the temperature detection unit 100 is furtherconnected to the inverting input terminal of the voltage comparator unit520. The non-inverting input terminal of the voltage comparator unit 520is applied with a reference voltage V_(k4) lower than the referencevoltage V_(k3) applied to the voltage comparator unit 510. The voltagecomparator unit 520, a generator (not shown) for generating thereference voltage V_(k4), and the temperature detection unit 100constitute a second temperature detection unit. In the secondtemperature detection unit, when the temperature detected by thethermistor Th is increased, and the output V_(t) from the temperatureconversion circuit unit 120 is decreased and reaches V_(k4), the outputfrom the voltage comparator unit 520 is inverted from low level to highlevel, thereby generating a detection output indicating that thetemperature of the battery 10 has reached a second setting temperaturecorresponding to the setting value V_(k4).

The output terminals of the voltage comparator units 500, 510, and 520are respectively connected to input terminals f, g, and h of the controlcircuit unit 850. FIG. 16 shows a circuit arrangement of the controlcircuit unit 850. In FIG. 16, the input terminal f is connected to thefirst input terminal of a first OR gate 860A and the first inputterminal of a second OR gate 860B, the input terminal g is connected tothe second input terminal of the OR gate 860A, and the input terminal his connected to the second input terminal of the OR gate 860B. Theoutput terminal of the OR gate 860A is connected to a reset inputterminal R of a first flip-flop 870A.

A start pulse generated in synchronism with a power-on or switch-onoperation is applied to the set input terminal S of the flip-flop 870A.When the start pulse is applied to the set input terminal S of theflip-flop 870A, a non-inverted output Q from the flip-flop 870A goesfrom low level to high level, and an inverted output P goes from highlevel to low level. The output from the OR gate 860B is connected to areset input terminal R of a second flip-flop 870B, and a set inputterminal S of the second flip-flop 870B receives the inverted output Pfrom the flip-flop 870A via a single pulse generator unit 880. Thesingle pulse generator unit 880 comprises, e.g., a monostablemultivibrator.

An output from a CR time constant circuit 890 as a circuit for detectinga power-on state is connected to the third input terminal of the OR gate860A, and the third input terminal of the OR gate 860B.

The non-inverted output Q from the flip-flop 870A is connected to acontrol terminal of the switch SW1 of the switching circuit 320 via anoutput terminal i of the control circuit unit 850, and the non-invertedoutput Q of the flip-flop 870B is connected to a control terminal of theswitch SW2 of the switching circuit 320 via an output terminal j of thecontrol circuit unit 850. These outputs are used for switching ON/OFFstates of the switches SW1 and SW2.

The OR gates 860A and 860B, the flip-flops 870A and 870B, the singlepulse generator unit 880, and the CR time constant circuit 890constitute the control circuit unit 850 for charge control.

The operation of the charging circuit shown in FIG. 15 will be describedbelow with reference to FIG. 16, FIGS. 17A to 17C and FIGS. 18A to 18C.

When the power switch of the charging circuit is turned on, the CR timeconstant circuit 890 generates a pulse having a pulse width determinedby a time constant of C (capacitor) and R (resistor). The pulse is inputto the reset input terminal R of the flip-flop 870A via the OR gate860A, and is also input to the reset input terminal R of the flip-flop870B via the OR gate 860B. As a result, the outputs Q of the flip-flops870A and 870B go to low level. In this case, both the switches SW1 andSW2 of the switching circuit 320 are set in an OFF state, and nocharging current is supplied from the first or second charging source200A or 200B to the battery 10.

When the start pulse generated in synchronism with a power-on orswitch-on operation is input to the set input terminal S of theflip-flop 870A, the output Q from the flip-flop 870A goes to high level.Thus, the switch SW1 of the switching circuit 320 is set in an ON state,and a first charging period is started. During the first chargingperiod, the battery 10 is subjected to fast charging with a current I₁from the charging source 200A.

As shown in FIG. 17A, although the temperature of the battery 10 isslowly increased in the initial or middle period of charging, it beginsto abruptly increase in the final period of charging. An output of avoltage value corresponding to a rate of change in temperature of thebattery 10 with respect to the charging time is obtained by thetemperature change rate detection unit 450, and the output from thetemperature change rate detection unit 450 is input to the voltagecomparator unit 500. The voltage comparator unit 500 compares the outputfrom the temperature change rate detection unit 450 with a settingvalue, and generates an inverted output at time t₁ in FIG. 17B. Theinverted output is input to the reset input terminal R of the flip-flop870A via the OR gate 860A, and is also input to the reset input terminalR of the flip-flop 870B via the OR gate 860B. For this reason, thenon-inverted outputs Q of the flip-flops 870A and 870B go to low level,and the switches SW1 and SW2 of the switching circuit 320 are set in anOFF state. Therefore, no charging current is supplied from the first orsecond charging source 200A or 200B to the battery 10, thus stoppingcharging.

When the non-inverted output Q from the flip-flop 870A goes to lowlevel, since its inverted output P goes to high level at the same time,a pulse is generated from the single pulse generator unit 880, and isinput to the set input terminal S of the flip-flop 870B. The outputpulse width of the single pulse generator unit 880 is normally selectedto fall within a range between 1 ms and 1 s. If the flip-flop 870B is areset priority type flip-flop, since the inverted output from thevoltage comparator unit 500 is applied to the reset input terminal R ofthe flip-flop 870B via the input terminal f of the control circuit unit850 and the OR gate 860B, even when the pulse from the single pulsegenerator unit 880 is input to the set input terminal S of the flip-flop870B, the non-inverted output Q is kept at low level. For this reason,the switch SW2 of the switching circuit 320 is kept in an OFF state, andcharging is kept stopped.

When the inverted output from the voltage comparator unit 500 is stoppedwhile the pulse is applied to the set input terminal S of the flip-flop870B, i.e., when the output from the voltage comparator unit 500 isinverted from high level to low level, the non-inverted output Q fromthe flip-flop 870B goes to high level. However, in practice, since thereis a time delay of several seconds to several tens of seconds (dependingon the type of battery 10, the mounting state, the charging current, andthe like) from when charging is stopped until the rate of increase intemperature is decreased below a setting value, the non-inverted outputQ from the flip-flop 870B will never go to high level.

If the flip-flop 870B is a set priority type flip-flop, since thenon-inverted output Q is kept at high level while the pulse from thesingle pulse generator unit 880 is applied to the set input terminal Sof the flip-flop 870B, the switch SW2 in the switching circuit 320 isset in an ON state, and a second charging period is started. However,since the output pulse width of the single pulse generator unit 880 isnormally selected to fall within a range between 1 ms and 1 s, asdescribed above, and it is a negligible time in comparison with thecharging time, no problem is posed even if the second charging period istemporarily started.

As described above, even when the inverted output is generated from thevoltage comparator unit 500 during the second charging period, thesecond charging period is not substantially started by stopping chargingwithin zero time or by ending the second charging period within a veryshort period of time (almost zero time) as compared to the chargingperiod.

In the above-mentioned operations, charging is performed at low ornormal temperature. When charging is performed at high temperature, thefollowing operations are performed. FIGS. 18A to 18C show operationwaveforms of the respective units when charging is performed at hightemperature.

During the first charging period, since the battery 10 slightlygenerates heat, when charging is performed at high temperature, therelationship between an output V_(t) ' from the temperature change ratedetection unit 450 and a setting value V_(k2) satisfies V_(t) '<V_(k2),i.e., the voltage comparator unit 500 does not generate an invertedoutput. When V_(t) <V_(k3) is satisfied at time t₁ shown in FIG. 18Abefore the end of charging, the voltage comparator unit 510 generates adetection output indicating that the battery temperature has reached afirst setting temperature (T₁).

Since the detection output is input to the reset input terminal R of theflip-flop 870A via the input terminal g of the control circuit unit 850and the OR gate 860A, the non-inverted output Q from the flip-flop 870Agoes to low level. Thus, the switch SW1 of the switching circuit 320 isset in an OFF state, and the first charging period is ended.

Simultaneously with the end of the first charging period, the singlepulse generator unit 880 is driven in response to the inverted output Pfrom the flip-flop 870A, thus generating a pulse. Since the non-invertedoutput Q from the flip-flop 870B goes to high level in response to thispulse, the switch SW2 of the switching circuit 320 is set in an ONstate, thus starting the second charging period.

During the second charging period, the battery 10 is charged by thesecond charging source 200B via the switch SW2. During the secondcharging period, since the battery is slowly charged with a current I₂lower than that during the first charging period, the temperature riseof the battery 10 becomes slow. When the charging further progresses,the temperature of the battery 10 begins to slowly increase again.

Upon an increase in temperature, when the output V_(t) from thetemperature conversion circuit unit 120 satisfies V_(t) <V_(k4), i.e.,at time t₂ in FIG. 18A, one, which is generated earlier, of a detectionoutput generated from the voltage comparator unit 520 and indicatingthat the temperature of the battery 10 has reached a second settingtemperature (T₂), and the inverted output from the voltage comparatorunit 500 when the rate of increase in temperature of the battery 10 isincreased and the output V_(t) ' from the temperature change ratedetection circuit 450 is increased accordingly, is input to the resetinput terminal R of the flip-flop 870B via the OR gate 860B. For thisreason, the non-inverted output Q from the flip-flop 870B goes to lowlevel, and the switch SW2 of the switching circuit 320 is set in an OFFstate. As a result, no charging current is supplied from the first orsecond charging source 200A or 200B to the battery 10, and the chargingoperation is stopped.

In the above description of the operations, when the output from thetemperature change rate detection unit 450 is increased, and the voltagecomparator unit 500 generates an inverted output during the firstcharging period, the second charging period is stopped within zero oralmost zero time. Instead, the second charging period may be started inresponse to one, generated earlier, of a detection output from the firsttemperature detection unit (the inverted output from the voltagecomparator unit 510) and the inverted output from the voltage comparatorunit 500, and may be ended in response to one, generated earlier, of adetection output from the second temperature detection unit (theinverted output from the voltage comparator unit 520) and the invertedoutput from the voltage comparator unit 500.

For this purpose, the flip-flop 870B shown in FIG. 15 may comprise a setpriority type flip-flop, and the output pulse width of the single pulsegenerator unit 880 may be prolonged. When the first charging periodtransits to the second charging period, the charging current isdecreased, and the amount of heat generated by the battery 10 isdecreased. Therefore, the temperature of the battery 10 is decreased.However, since there is a time delay until the decrease in temperatureis detected by the temperature sensor 110, the output pulse width of thesingle pulse generator unit 880 may be set to be equal to or larger thanthe above-mentioned time delay. Thus, the charging amount can beincreased.

The end of the second charging period may be detected by using only thedetection output from the second temperature detection unit. In thiscase, as shown in, e.g., FIG. 19, only the input terminal h of thecontrol circuit unit 850, and the output from the CR time constantcircuit 890 may be input to the OR gate 860B. In this manner, thecharging amount can be increased when a battery which hascharacteristics in that a temperature rise becomes abrupt at arelatively early timing in the final period of charging is to be chargedat low temperature.

Furthermore, when charging is also ended in response to the output fromthe voltage comparator unit 500 during the second charging period, thereference voltage V_(k2) may have different voltage values during thefirst and second charging periods. Since the charging current during thesecond charging period is lower than that in the first charging period,the rate of increase in temperature of the battery 10 in the finalperiod of charging during the second charging period is also smallerthan that during the first charging period. When the reference voltageV_(k2) during the second charging period is set to be lower than thatduring the first charging period, reliability and safety can be furtherimproved.

FIG. 20 is a circuit diagram showing a charging circuit according to thefifth embodiment of the present invention.

Differences between this embodiment and the first embodiment are that aplurality of temperature detection units 100 are arranged, and an ORgate and a flip-flop are arranged between a voltage comparator unit anda charge control circuit unit while omitting the differential circuitunit 400.

In FIG. 20, a plurality of batteries 10A and 10B are connected in serieswith a charging source 200 via a change control circuit unit 300.

Temperature detection units 100A and 100B for detecting the temperaturesof the batteries 10A and 10B and converting the detected temperaturesinto voltages are the same as that in the first embodiment. The outputsfrom the temperature detection units 100A and 100B are respectivelyconnected to voltage comparator units 500A and 500B.

The outputs from the voltage comparator units 500A and 500B arerespectively input to two input terminals of an OR gate 730, and theoutput terminal of the OR gate 730 is connected to a reset terminal R ofa flip-flop circuit unit 310. A set terminal S of the flip-flop circuitunit 310 is connected to a start pulse application terminal. Anon-inverted output terminal Q of the flip-flop circuit unit 310 isconnected to a charge control circuit unit 300. The OR gate 730, theflip-flop circuit unit 310, and the charge control circuit 300constitute a control unit for controlling charging of the batteries 10Aand 10B in response to a detection output, generated earlier, of thosefrom the voltage comparator units 500A and 500B.

The operations of the charging circuit shown in FIG. 20 will bedescribed below with reference to charging characteristic graphs shownin FIGS. 21A to 21F. FIG. 21A shows voltages (battery voltages) of thebatteries 10A and 10B, FIG. 21B shows temperatures (batterytemperatures) of the batteries 10A and 10B, FIG. 21C shows outputsV_(t1) and V_(t2) from temperature conversion circuit units 120A and120B, FIG. 21D shows an output from the voltage comparator unit 500A,FIG. 21E shows an output from the voltage comparator unit 500B, and FIG.21F shows an output from the OR gate 730.

In general, the voltages of the batteries 10A and 10B are increasedimmediately in the initial period of charging, are increased slowly inthe middle period of charging, and show a peak in the final period ofcharging, as shown in FIG. 21A. The temperatures of the batteries 10Aand 10B are slowly increased over the initial and middle periods ofcharging, and are then immediately increased in the final period ofcharging, as shown in FIG. 21B. In this embodiment, since the battery10A has a smaller electrical capacity than that of the battery 10B, thebattery temperature of the battery 10B is assumed to immediatelyincrease earlier than the battery 10A.

When a start pulse generated in synchronism with a power-on or aswitch-on operation of the charging circuit is applied to the setterminal S of the flip-flop circuit unit 310, the output terminal Q ofthe flip-flop circuit unit 310 goes to high level, and the chargecontrol circuit unit 300 is set in a fast charging state. In this state,a large current is supplied from the charging source 200 to thebatteries 10A and 10B, thus starting fast charging.

When the charging operation continues, and reaches the final period ofcharging, as shown in FIG. 21B, the temperature of the battery 10Ahaving a smaller electrical capacity begins to abruptly increase priorto the battery 10B. When the charging operation further continues, thetemperature of the battery 10B begins to abruptly increase. As shown inFIG. 21C, the output value V_(t1) from the temperature conversioncircuit unit 120A is decreased first, and then, the output value V_(t2)of the temperature conversion circuit 120B is decreased. The outputvalues V_(t1) and V_(t2) are compared with a reference voltage V_(k2)corresponding to a setting temperature T_(k) by the voltage comparatorunits 500A and 500B. Based on the comparison results, V_(t1) <V_(k2) issatisfied at time t=t₁, as shown in FIG. 21D, and the output from thevoltage comparator unit 500A goes to high level. As shown in FIG. 21E,V_(t2) <V_(k2) is satisfied at time t=t₂, and the output from thevoltage comparator unit 500B goes to high level.

The outputs from the voltage comparator units 500A and 500B are input tothe two input terminals of the OR gate 730. Since t₁ <t₂, the outputfrom the OR gate 730 goes to high level at time t=t₁, as shown in FIG.21F. When the output from the OR gate 730 goes to high level, the outputterminal Q of the flip-flop circuit unit 310 goes to low level, and thecharge control circuit unit 300 is set in the charge control state. As aresult, the charging operation is stopped, or the charging current isdecreased.

A modification of the fifth embodiment of the present invention will bedescribed below. FIG. 22 is a circuit diagram showing a charging circuitaccording to a modification of the fifth embodiment of the presentinvention. In FIG. 22, the charging source 200, the batteries 10A and10B, and the temperature detection units 100A and 100B are the same asthose in FIG. 20. The temperature detection unit shown in FIG. 20 isassumed to have the circuit shown in FIG. 4. In a description of thismodification, however, the temperature detection unit is assumed to havethe circuit shown in FIG. 2.

The output terminals of the temperature conversion circuit units 120Aand 120B are connected to the two input terminals of a signal processingcircuit unit 150. The signal processing circuit unit 150 is a circuitfor outputting a voltage V_(tm) corresponding to a higher one ofvoltages input to the two input terminals. More specifically, thevoltage V_(tm) corresponding to a higher one of the temperaturesdetected by the temperature detection units 100A and 100B is output fromthe output terminal of the signal processing circuit unit 150. As thetemperature is increased, the voltage V_(tm) is decreased.

As shown in FIG. 23, the signal processing circuit unit 150 comprisestwo ideal diode circuit units 160A and 160B. The ideal diode circuitunit 160A comprises resistors R₃ and R₄, an operational amplifier A₁,and diodes D₁ and D₂. The inverting input terminal of the operationalamplifier A₁ is connected to an input terminal d₁ of the signalprocessing circuit unit 150 via the resistor R₃, is also connected tothe output terminal of the operational amplifier A₁ via the diode D₁,and is then connected to the output terminal of the signal processingcircuit unit 150 via the resistor R₄. The non-inverting input terminalof the operational amplifier A₁ is grounded, and the output terminalthereof is connected to the output terminal of the signal processingcircuit unit 150 via the diode D₂. The ideal diode circuit unit 160Bcomprises resistors R₃ and R₆, an operational amplifier A₂, and diodesD₃ and D₄, which are connected in the same manner as in the ideal diodecircuit unit 160A.

If voltages applied to input terminals d₁ and d₂ of the signalprocessing circuit unit 150 are represented by V_(t1) and V_(t2), andthe resistances of the resistors R₃, R₄, R₅, and R₆ are respectivelyrepresented by R₃, R₄, R₅, and R₆, individual output voltages of theideal diode circuit units 160A and 160B (output voltages obtained whentheir output terminals are not connected to each other as shown in FIG.22) are respectively given by:

    -V.sub.t1 ·(R.sub.4 /R.sub.3)

    -V.sub.t2 ·(R.sub.6 /R.sub.5)

If R₃ =R₄ and R₅ =R₆, the individual output voltages of the ideal diodecircuit units 160A and 160B are respectively -V_(t1) and -V_(t2).

Since the electrical capacity of the battery 10A is smaller than that ofthe battery 10B, the battery temperature of the battery 10A is abruptlyincreased earlier than the battery 10B in the final period of charging.Therefore, since V_(t1) >V_(t2) >0, the output voltage from the idealdiode circuit unit 160A becomes lower than that from the ideal diodecircuit unit 160B. As a result, when the output terminals of the idealdiode circuit units 160A and 160B are connected to each other, as shownin FIG. 22, a lower voltage -V_(t1) is output. More specifically, avoltage having a polarity opposite to a voltage corresponding to ahigher one of the temperatures detected by the temperature detectionunits 100A and 100B is output from the signal processing circuit unit150 as the output voltage V_(tm).

The output from the signal processing circuit unit 150 is input to theinverting input terminal of the voltage comparator unit 500. Thenon-inverting input terminal of the voltage comparator unit 500 isconnected to an application terminal of a reference voltage V_(k2)corresponding to a setting temperature. When the output voltage valueV_(tm) exceeds the reference voltage V_(k2), the output from the voltagecomparator unit 500 is inverted to high level.

The output from the voltage comparator unit 500 is connected to thereset terminal R of the flip-flop circuit unit 310. The set terminal Sof the flip-flop circuit unit 310 is connected to a start pulseapplication terminal. The non-inverted output terminal Q of theflip-flop circuit unit 310 is connected to the control terminal of thecharge control circuit unit 300. The charge control circuit unit 300 hasthe same arrangement as that in the fifth embodiment. The voltagecomparator unit 500, the flip-flop circuit unit 310, and the chargecontrol circuit unit 300 constitute a control unit for controlling thecharging operations of the batteries 10A and 10B when the output fromthe signal processing circuit unit 150 reaches a setting value.

The operation of the charging circuit shown in FIG. 22 will be describedbelow with reference to charging characteristic graphs shown in FIGS.24A to 24E. FIG. 24A shows changes in voltages (battery voltages) of thebatteries 10A and 10B over time after charging is started, FIG. 24Bshows changes in temperatures (battery temperatures) of the batteries10A and 10B over time after charging is started, FIG. 24C shows changesin outputs V_(t1) and V_(t2) from the temperature conversion circuitunits 120A and 120B over time after charging is started, FIG. 24D showsa change in output from the signal processing circuit unit 150 over timeafter charging is started, and FIG. 24E shows a change in output fromthe voltage comparator unit 500 over time after charging is started.

Like in the fifth embodiment shown in FIG. 20, as shown in FIG. 24A, thevoltages of the batteries 10A and 10B are abruptly increased in theinitial period of charging, are slowly increased in the middle period ofcharging, and show a peak in the final period of charging. As shown inFIG. 24B, the temperatures of the batteries 10A and 10B are slowlyincreased over the initial and middle periods of charging, and areabruptly increased in the final period of charging. In this embodiment,since the battery 10A has a smaller electrical capacity than that of thebattery 10B, the battery temperature of the battery 10A is abruptlyincreased earlier than the battery 10B.

When a start pulse generated in response to a power-on or switch-onoperation of the charging circuit is applied to the set terminal S ofthe flip-flop circuit unit 310, the output terminal Q of the flip-flopcircuit unit 310 goes to high level, and the charge control circuit unit300 is set in a fast charging state. In the fast charging state, a largecurrent is supplied from the charging source 200 to the batteries 10Aand 10B, thus starting fast charging.

When the charging operation continues, and the final period of chargingis reached, as shown in FIG. 24B, the temperature of the battery 10Ahaving a smaller electrical capacity begins to abruptly increase priorto the battery 10B. When the charging operation further continues, thetemperature of the battery 10B begins to abruptly increase. As shown inFIG. 24C, the output value V_(t1) from the temperature conversioncircuit unit 120A is abruptly increased first, and then, the outputvalue V_(t2) from the temperature conversion circuit unit 120B isabruptly increased. Therefore, V_(t1) >V_(t2) is satisfied, and avoltage -V_(t1) appears at the output terminal of the signal processingcircuit unit 150 as the output voltage V_(tm). The voltage comparatorunit 500 compares the output voltage V_(tm) (-V_(t1)) from the signalprocessing circuit unit 150 with the reference voltage V_(k2)corresponding to a setting temperature T_(k), and when V_(tm) <V_(k2) issatisfied, the output from the voltage comparator unit 500 is invertedto high level. More specifically, when one of the temperatures detectedby the temperature detection units 100A and 100B reaches the settingtemperature corresponding to the reference voltage V_(k2), the voltagecomparator unit 500 generates an inverted output.

Since the inverted output from the voltage comparator unit 500 is inputto the reset terminal R of the flip-flop circuit unit 310, the outputterminal Q of the flip-flop circuit unit 310 goes to low level, and thecharge control circuit unit 300 is set in the charge control state. Inthe charge control state, no current is supplied from the chargingsource 200 to the batteries 10A and 10B, and the charging operation isstopped or the charging current is decreased.

FIG. 25 is a block diagram showing a charging circuit according to thesixth embodiment of the present invention.

Differences between this embodiment and the first embodiment are that anA/D converter unit 460 is used in place of the differential circuitunit, and a CPU 350, a timer circuit unit 360, and a memory 370 are usedin place of the voltage comparator unit 500 and the charge controlcircuit unit 300.

In FIG. 25, a charging source 200 performs fast charging with a largecharging current in an initial period of charging. Thereafter, when theCPU (microcomputer) 350 determines that fast charging is ended, thecharging source 200 decreases the charging current and starts quickcharging or trickle charging.

The temperature of a battery 10 is detected by a temperature detectionunit 100, and is converted into a voltage. The voltage is output to theA/D converter unit 460. The output voltage input to the A/D converterunit 460 is converted into, e.g., an 8-bit digital value by the A/Dconverter unit 460, and the digital value is output as temperature data.The temperature data output from the A/D converter unit 460 is fetchedby the CPU 350 in synchronism with a timing signal from the timercircuit unit 360 at a predetermined time interval (m), and is stored inthe memory 370.

The memory 370 controlled by the CPU 350 comprises a programmable memoryelement such as a RAM, and has a plurality of (K) memory areas M₀ toM_(K-1), as shown in FIG. 26. The memory 370 stores K temperature dataat the m-time intervals from the A/D converter unit 460.

when the charging operation is started, the memory areas M₀ to M_(K-1)are reset, and when a temperature measurement is started, firsttemperature data output from the A/D converter unit 460 is written inthe memory area M₀. When new temperature data is output after an elapseof the m time, the data in the memory area M₀ is shifted to the memoryarea M₁ simultaneously with the data output operation, and the newtemperature data is written in the memory area M₀. Similarly, every timenew temperature data is output from the A/D converter unit 460, thetemperature data in the respective memory areas are shifted to the nextmemory areas, and finally, temperature data for K×m time are stored inthe memory areas M₀ to M_(K-1). After the temperature data are stored inall the memory areas M₀ to M_(K-1), every time new temperature data isoutput from the A/D converter unit 460, the oldest temperature datastored in the memory area M_(K-1) is erased, and at the same time, thecontents of the memory areas M₀ to M_(K-2) are shifted to the nextmemory areas M₁ to M_(K-1). Thus, the new temperature data is stored inthe memory area M₀, thereby updating the storage contents.

If temperature data stored in the memory areas M₀ to M_(K-1) arerespectively represented by T₀ to T_(K-1), the CPU 350 calculatesdifference data (to be referred to as temperature difference datahereinafter) A₁ to A_(K-1) temperature data T₁ to T_(K-1) as follows(see (a) in FIG. 27):

    ______________________________________                                                   T.sub.0 - T.sub.1 = A.sub.1                                                   T.sub.0 - T.sub.2 = A.sub.2                                                   T.sub.0 - T.sub.3 = A.sub.3                                                   . . .                                                                         T.sub.0 - T.sub.K-2 = A.sub.K-2                                               T.sub.0 - T.sub.K-1 = A.sub.K-1                                    ______________________________________                                    

The temperature difference data A₁ to A_(K-1) correspond to the rates ofincrease in temperature at the respective timings at the m-timeintervals. The CPU 350 checks if each of the temperature difference dataA₁ to A_(K-1) exceeds a predetermined value α, and if the number oftemperature data exceeding the predetermined value α reaches apredetermined value q (1≦q≦K-1), the CPU 360 determines that the fastcharging is ended. When the CPU 350 determines the end of fast charging,it controls the charging source 200 to decrease the charging current,and causes it to start quick charging or trickle charging.

In the above description, as shown in (a) in FIG. 27, the latesttemperature data T 0 of the temperature data T₀ to T_(K-1) is used asreference data. However, as shown in (b) in FIG. 27, temperaturedifference data may be obtained using the oldest temperature dataT_(K-1) as reference data. In this case, if temperature difference dataare represented by B₁ to B_(K-1), they can be calculated as follows:

    ______________________________________                                                  T.sub.0 - T.sub.K-1 = B.sub.1                                                 T.sub.1 - T.sub.K-1 = B.sub.2                                                 T.sub.2 - T.sub.K-1 = B.sub.3                                                 . . .                                                                         T.sub.K-3 - T.sub.K-1 = B.sub.K-2                                             T.sub.K-2 - T.sub.K-1 = B.sub.K-1                                   ______________________________________                                    

The number of temperature data corresponding to temperature differencedata exceeding the predetermined value &A in (a) in FIG. 27 is equal toor larger than that in (b) in FIG. 27, and basically the same result canbe obtained. The methods shown in (a) and (b) in FIG. 27 can be selecteddepending on the characteristics of the battery 10. More specifically,when a battery in which an abrupt temperature rise begins relativelyearlier in the final period of charging is to be charged, the methodshown in (b) in FIG. 27 can be used. On the other hand, when a batteryin which an abrupt temperature rise begins later in the final period ofcharging is to be charged, the method shown in (a) in FIG. 27 can beused. As reference temperature data for obtaining temperature differencedata, temperature data other than data T₀ and T_(K-1) may be used.

FIG. 28 is a block diagram showing a secondary battery charging circuitaccording to the seventh embodiment of the present invention.

Differences between this embodiment and the first embodiment are that aswitching circuit unit 320 is arranged in place of the control circuitunit, and a control circuit unit 855 is added between a voltagecomparator unit 500 and a switching circuit unit 320. Furthermore,voltage comparator units 501, 502, and 503 are arranged between thecontrol circuit unit 855, and a temperature detection unit 100, and aNOR gate 721, an OR gate 722, and first to fourth timer circuit units711 to 714 are arranged.

The operation of this embodiment will be described below with referenceto FIGS. 28 and 29.

In FIG. 28, a battery 10 is selectively connected to first, second, andthird charging sources 200A, 200B, and 200C via a switching circuit unit320 including three switches SW1, SW2, and SW3. The switches SW1, SW2,and SW3 comprise, e.g., transistors, thyristors, relays, or the like.The first charging source 200A is used for fast charging, the secondcharging source 200B is used for quick charging, and the third chargingsource 200C is used for trickle charging. The output currents from thesecharging sources are as follows. The output current from the secondcharging source 200B is smaller than that from the first charging source200A, and the output current from the third charging source 200C issmaller than that from the second charging source 200B.

Like in the first embodiment, the temperature of the battery 10 isdetected, and a detection signal is converted into an electrical signal.The electrical signal is converted into a rate of change in temperatureby, e.g., differentiating the signal, and thereafter, the rate iscompared with a setting value.

The output from the temperature detection unit 100 is connected to theinverting input terminals of the voltage comparator units 501, 502, and503 in addition to a temperature change rate detection circuit 400. Thenon-inverting input terminals of the voltage comparator units 501, 502,and 503 are respectively applied with reference voltages V_(k2), V_(k3),and V_(k4). These reference voltages can be set. The temperaturedetection unit 100 and the voltage comparator unit 501 constitute afirst temperature detection unit, the temperature detection unit 100 andthe voltage comparator unit 502 constitute a second temperaturedetection unit, and the temperature detection unit 100 and the voltagecomparator unit 503 constitute a third temperature detection unit.

In the first temperature detection unit, when the temperature of thebattery 10 is increased, and the output voltage V_(t) from thetemperature detection unit 100 is decreased and reaches the referencevoltage V_(k2), the output from the voltage comparator unit 501 isinverted from low level to high level. Thus, the first temperaturedetection unit generates a detection output indicating that thetemperature of the battery 10 has reached a first setting temperaturecorresponding to the reference voltage V_(k2).

The second and third temperature detection units perform the sameoperations as in the first temperature detection unit, and generatedetection outputs indicating that the temperature of the battery 10 hasreached second and third setting temperatures corresponding to thereference voltages V_(k3) and V_(k4), respectively.

The output from the voltage comparator unit 500 is input to an inputterminal a of the control circuit unit 855 via one input terminal of theNOR gate 721 having two input terminals, and the outputs from thevoltage comparator units 501, 502, and 503 are respectively input toinput terminals b, c, and d of the control circuit unit 855.

A start pulse is input to the fourth timer circuit unit 714 via an inputterminal f of the control circuit unit 855, and one input terminal ofthe OR gate 722 having two input terminals, and the output from thefourth timer circuit unit 714 is input to the other input terminal ofthe NOR gate 721. The other input terminal of the OR gate 722 isconnected to an input terminal h of the control circuit unit 855. TheNOR gate 721, the OR gate 722, and the fourth timer circuit unit 714constitute a circuit for inhibiting charge control upon generation of aninverted output for a predetermined period of time from the beginning ofa first charging period, and from the beginning of a second chargingperiod.

Output terminals g, h, and i of the control circuit unit 855 arerespectively connected to the control terminals of the switches SW1,SW2, and SW3 of the switching circuit unit 320. The output terminals g,h, and i of the control circuit unit 855 are also respectively connectedto the first, second, and third timer circuit units 711, 712, and 713.The output terminals of the first to third timer circuit units 711 to713 are connected to the control circuit unit 855.

Charge control is performed as follows.

As shown in FIG. 29, when a charging operation is started, the battery10 is tested. If it is determined based on the test result of thebattery 10 that the battery voltage falls outside a predetermined valuerange or that ambient temperature falls outside a predetermined range,the charging operation is stopped. As a result of the battery test, ifno problem is found, a start pulse is input to the input terminal f ofthe control circuit unit 855, thus starting fast charging in the firstcharging period. At this time, an output is generated from the outputterminal g of the control circuit unit 855 to turn on the switch SW1 ofthe switching circuit unit 320, and to start the first timer circuitunit. The start pulse is simultaneously input to the OR gate 722 tostart the fourth timer circuit unit 714. Since the output from the NORgate 721 maintains low level while the output from the fourth timercircuit unit 714 is kept at high level, the input to the input terminala of the control circuit unit 855 is kept at low level. Thus, even whenthe output from the temperature change rate detection circuit 400 goesto low level due to a voltage drift immediately after the beginning ofthe charging operation, the first charging period can be maintained, andthe second charging period will not be started.

The end of the first charging period is determined based on one of thefollowing three conditions.

1) In the final period of charging, when the output from the voltagecomparator unit 500 is inverted from high level to low level since therate of change in temperature is abruptly increased, and an output V_(t)' from the temperature change rate detection circuit 400 exceeds areference voltage V_(k1), the output from the NOR gate 721 goes to highlevel. When the high-level output is input to the input terminal a ofthe control circuit unit 855, the switch SW1 of the switching circuitunit 320 is turned off in response to a signal from the output terminalg of the control circuit unit 855.

2) In the final period of charging, when the output from the voltagecomparator unit 501 is inverted from high level to low level since thetemperature of the battery 10 is increased, and a voltage output V_(t)from the temperature detection unit 100 exceeds a reference voltageV_(k2), the inverted output is input to the input terminal b of thecontrol circuit unit 855. Thus, the switch SW1 of the switching circuitunit 320 is turned off in response to a signal from the output terminalg of the control circuit unit 855.

3) Upon an elapse of a setting time of the first timer circuit unit 711,which is started simultaneously with the start of the first chargingperiod, the output from the first timer circuit unit 711 is input to theinput terminal j of the control circuit unit 855. Thus, the switch SW1of the switching circuit unit 320 is turned off in response to a signalfrom the output terminal g of the control circuit unit 855.

when one of the above-mentioned three conditions is satisfied, and theswitch SW1 is turned off, a control signal is generated from the outputterminal h of the control circuit unit 855, and the switch SW2 is turnedon. At the same time, the second timer circuit unit 712 is started, andquick charging in the second charging period is started.

Since the output signal from the output terminal h of the controlcircuit unit 855 is input to the OR gate 722 simultaneously with thestart of the second charging period for a predetermined period of timefrom the beginning of quick charging as the second charging period likein a state immediately after the beginning of the first charging period,the second charging period is inhibited from being ended. The reason forthis is the same as that for inhibiting the first charging period frombeing ended for a predetermined period of time from the beginning. Sincea change in battery temperature immediately after the first chargingperiod transits to the second charging period is the same as that at thebeginning of fast charging, the end of the second charging period iscontrolled by the following three conditions like in the end conditionsof the first charging period.

1) In the final period of charging, when the output from the voltagecomparator unit 500 is inverted from high level to low level since therate of change in temperature is abruptly increased, and an output V_(t)' from the temperature change rate detection circuit 400 exceeds areference voltage V_(k1), the output from the NOR gate 721 goes to highlevel. When the high-level output is input to the input terminal a ofthe control circuit unit 855, the switch SW2 of the switching circuitunit 320 is turned off in response to a signal from the output terminalh of the control circuit unit 855.

2) In the final period of charging, when the output from the voltagecomparator unit 502 is inverted from high level to low level since thetemperature of the battery 10 is increased, and a voltage output V_(t)from the temperature detection unit 100 exceeds a reference voltageV_(k3), the inverted output is input to the input terminal c of thecontrol circuit unit 855. Thus, the switch SW2 of the switching circuitunit 320 is turned off in response to a signal from the output terminalh of the control circuit unit 855.

3) Upon an elapse of a setting time of the second timer circuit unit712, which is started simultaneously with the start of the secondcharging period, the output from the second timer circuit unit 712 isinput to the input terminal k of the control circuit unit 855. Thus, theswitch SW2 of the switching circuit unit 320 is turned off in responseto a signal from the output terminal h of the control circuit unit 855.

when one of the above-mentioned three conditions is satisfied, and theswitch SW2 is turned off, a control signal is generated from the outputterminal i of the control circuit unit 855 to turn on the switch SW3,and to start the third timer circuit unit 713, thus starting tricklecharging in the third charging period.

Since the trickle charging is performed in the third charging period,almost no abrupt increase in temperature is observed in the final periodof charging. Therefore, the end of the third charging period iscontrolled by the following two conditions.

1) When the error occurs in the charging circuit and the output from thevoltage comparator unit 503 is inverted from high level to low levelsince the temperature of the battery 10 is increased, and a voltageoutput V_(t) from the temperature detection unit 100 exceeds a referencevoltage V_(k4), the inverted output is input to the input terminal d ofthe control circuit unit 855. Thus, the switch SW3 of the switchingcircuit unit 320 is turned off in response to a signal from the outputterminal i of the control circuit unit 855.

2) Upon an elapse of a setting time of the third timer circuit unit 713,which is started simultaneously with the start of the third chargingperiod, the output from the third timer circuit unit 713 is input to theinput terminal k of the control circuit unit 855. Thus, the switch SW3of the switching circuit unit 320 is turned off in response to a signalfrom the output terminal i of the control circuit unit 855.

When one of the above-mentioned two conditions is satisfied, and theswitch SW3 is turned off, the charging operation by the circuit of thisembodiment is finished.

The reference voltage V k4 to be input to the voltage comparator unit503 may be determined as follows in relation to the voltage comparatorunits 501 and 502:

    (Temperature Upper Limit Setting Value of Trickle Charging)=2×(Temperature Upper Limit Setting Value of Quick Charging)-(Temperature Upper Limit Setting Value of Fast Charging)

Alternatively, the control circuit unit 855 may adjust the voltage tosatisfy the above relation.

As described above, in the seventh embodiment, since the chargingoperation is performed in the order of fast charging, quick charging,and trickle charging, a battery can be charged to almost 100% of itscapacity within a short period of time without overloading the battery.Furthermore, when some circuit components malfunction, and chargecontrol based on a change in temperature is disabled, since chargecontrol can be performed by the corresponding charge control timercircuit unit, a battery and equipment using the battery can be preventedfrom being damaged due to an abnormal increase in temperature byovercharging.

The present invention is not limited to the above embodiments, andvarious modifications may be made as follows.

In each of the first to seventh embodiments, a nickel-hydrogen batteryis used as a secondary battery. However, the present invention can beapplied to a case wherein other secondary batteries, such as anickel-cadmium battery, a lead-acid battery, and the like are used.

The temperature detection unit 100 comprises the temperature sensor(thermistor Th) 110, and the temperature conversion circuit unit 120,but may comprise another arrangement. For example, the temperaturedetection unit 100 may comprise a combination of a resistive temperaturesensor and a resistance-voltage converter, or may comprise anarrangement utilizing characteristics in that when a constant current isflowed, a forward voltage effect of a diode almost linearly changes upona change in temperature.

The respective units of each of the above embodiments are constituted byhardware components (except for the seventh embodiment). However, someor all of the units except for the temperature sensor may be realized ina software manner using, e.g., a microcomputer for executing processingbased on a program.

The charge control is performed based only on temperature data, but maybe executed in combination with another charge control method.

In the third embodiment, the flip-flop circuit unit may comprise a setpriority type flip-flop which is set in response to a charge startsignal, and is reset in response to a comparison output from thecomparator unit, and the signal identification circuit unit may outputthe charge start signal to the set input of the set priority typeflip-flop for a predetermined period of time after the comparator unitgenerates a comparison output.

In the fourth embodiment, the following arrangements may be available.

(1) Only the fast charging switch SW1 of the switching circuit unit 320is set in an ON state during the first charging period. However, thequick charging switch SW2 may also be set in an ON state. Morespecifically, a current as a combination of output currents from thefirst and second charging sources 200A and 200B may be used as a currentI 1. With this arrangement, the output capacity of the first chargingsource 200A can be decreased.

(2) The two different charging sources, i.e., the first and secondcharging sources 200A and 200B are prepared. However, only one chargingsource may be used, and an output current value may be varied betweenthe first and second charging periods under the external control.

(3) The charging current is completely cut off upon completion of thesecond charging period. However, a third charging source may beconnected to a node between the switches SW1 and SW2 of the switchingcircuit unit 320, or a resistor may be connected in parallel with theswitch SW1 or SW2, so that a battery is charged with a smaller currentI₃ by quick charging after the second charging period is ended.Normally, the current I₃ is set to be about 0.1 CmA. In this manner, abattery can be charged to near 100% of its capacity, and a decrease incharging amount due to self-discharging can be prevented.

In the fifth embodiment, the following arrangements are also available.

(1) In the embodiment shown in FIG. 20, the temperature detectioncircuit is constituted by the temperature conversion circuit units 120Aand 120B, and the voltage comparator units 500A and 500B. VoltagesV_(t1) and V_(t2) corresponding to the battery temperatures are comparedwith a reference voltage V_(k2), and when one battery temperaturereaches a setting value, the inverted output is generated. However, thefollowing arrangements may be adopted.

(a) Another temperature sensor for detecting ambient temperature of abattery may be arranged. An output from the temperature sensor isconverted into a voltage by a temperature conversion circuit, and when adifference between the output from this temperature conversion circuitand the output from the temperature conversion circuit unit 120A or 120Breaches a setting value, the inverted output may be generated. In thiscase, since charge control is performed when the battery temperature isincreased by a predetermined value with respect to ambient temperature,the charge control is not easily influenced by ambient temperature.

(b) The temperature detection circuit may comprise a memory circuit forstoring output voltages in the initial period of charging from thetemperature conversion circuit units 120A and 120B, and may generate aninverted output when the difference between the output stored in thememory circuit and the output from the temperature conversion circuitunit 120A or 120B reaches a setting value. In this case, since chargecontrol can be executed when the battery temperature is increased by apredetermined value from a temperature in the initial period ofcharging, the charge control is not easily influenced by ambienttemperature.

(c) The temperature detection circuit may generate an inverted outputwhen the rate of change in output from the temperature conversioncircuit unit 120A or 120B reaches a predetermined value. In this case,since charge control can be executed when the battery temperature isincreased by a predetermined value from a temperature in the initialperiod of charging, the charge control is not easily influenced byambient temperature.

(2) In the embodiment shown in FIG. 22, the output voltage V tm from thesignal processing circuit unit 150 is compared with the referencevoltage V_(k2) by the voltage comparator unit 500, and when the highestbattery temperature detected by the signal processing circuit unit 150reaches a setting value, an inverted output is generated. However, thefollowing arrangements (d) to (f) may be adopted.

(d) An output from another temperature sensor for detecting ambienttemperature of a battery may be converted into a voltage by atemperature conversion circuit, and when the difference between theoutput from this temperature conversion circuit and the output from thesignal processing circuit unit 150 reaches a setting value, an invertedoutput may be generated, thereby controlling a charging operation of thebattery. In this case, since charge control can be performed when thebattery temperature is increased by a predetermined value with respectto ambient tempera ture, the charge control is not easily influenced byambient temperature.

(e) A memory circuit for storing an output voltage in the initial periodof charging from the signal processing circuit unit 150 may be arranged,and the difference between the output from the memory circuit and theoutput from the signal processing circuit unit 150 may be detected. Whenthe difference reaches a setting value, an inverted output may begenerated to control a charging operation of a battery. In this case,since charge control can be executed when the battery temperature isincreased by a predetermined value from a temperature in the initialperiod of charging, the charge control is not easily influenced byambient temperature.

(f) The temperature detection circuit units 100A and 100B may generatedetection outputs which almost linearly change in accordance withchanges in temperature detected by the temperature sensors 110A and110B, and an inverted output may be generated when the rate of change inoutput from the signal processing circuit unit 150 reaches apredetermined value, thereby controlling a charging operation of abattery. In this case, since charge control can be executed when thebattery temperature begins to abruptly increase in the final period ofcharging, the charge control is not easily influenced by ambienttemperature, and overcharging can be prevented.

(3) In the embodiments shown in FIGS. 20 and 22, the followingarrangements are also available.

(a) Two sets of temperature sensors and temperature detection circuitunits are arranged. However, three or more sets of temperature sensorsand temperature detection circuit units may be arranged.

(b) The temperatures of batteries are individually measured. However, aplurality of batteries may be classified into a plurality of groupshaving similar thermal conditions, and the temperature may be measuredin units of groups.

(c) The charge control is performed by measuring the temperatures of aplurality of batteries connected in series with each other. However, acharging operation may be performed by measuring the temperatures ofdifferent portions of one secondary battery. In a large-capacitybattery, its vessel is large in size, and heat is often locallygenerated. The temperatures of a plurality of portions of such asecondary battery are measured, and charge control according to thepresent invention may be performed according to the measurement results.Thus, the charging operation can be performed without overcharging.

(d) The temperatures of a plurality of batteries connected in serieswith each other are measured to perform charge control. However, thepresent invention can be similarly applied to a plurality of batteriesconnected in parallel with each other, and to a plurality of batteriesconnected in series and parallel with each other.

Various other changes and modifications may be made within the spiritand scope of the invention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A secondary battery charging circuit comprising:afirst charging source for supplying a charging current to a secondarybattery; a secondary charging source for supplying a charging currentsmaller than the charging current supplied from said first chargingsource to said secondary battery; switching means for connecting saidfirst charging source to said secondary battery during a first chargingperiod, and connecting said second charging source to said secondarybattery during a second charging period; first temperature detectionmeans for detecting that a temperature of said secondary battery hasreached a first setting temperature, and generating a detection output;second temperature detection means for detecting that a temperature ofsaid secondary battery has reached a second setting temperature, andgenerating a detection output; temperature change rate detection meansfor detecting a rate of change in temperature of said secondary batterywith respect to time; comparator means for comparing an output valuefrom said temperature change rate detection means during a chargingoperation to said secondary battery with a setting value, and for, whenthe output value reaches the setting value, generating an invertedoutput; and control means for controlling a change of charging methods,and stop of the charging operation, said control means including atleast one of: means for, when the inverted output from said comparatormeans is generated during the first charging period, ending the firstcharging period so as not to substantially start the second chargingperiod, and for, when the detection output from said first temperaturedetection means is generated during the first charging period, startingthe second charging period, and ending the second charging period inresponse to one, generated earlier, of the detection output from saidsecond temperature detection means and the inverted output from saidcomparator means during the second charging period; means for startingthe second charging period in response to one, generated earlier, of thedetection output from said first temperature detection means and theinverted output from said comparator means during the first chargingperiod, and ending the second charging period in response to one,generated earlier, of the detection output from said second temperaturedetection means and the inverted output from said comparator meansduring the second charging period; and means for starting the secondcharging period in response to one, generated earlier, of the detectionoutput from said first temperature detection means and the invertedoutput from said comparator means during the first charging period, andending the second charging period in response to the detection outputfrom said second temperature detection means.